/sqt/ - stupid questions thread

>>8195990
Take mean, median and mode. Are they all the same? Its normal because central limit theorem.
Chi-square goodness-of-fit test to see if it's a normal distribution.
Whatever other unneccessary tests you wanna try.

Compute

m := E[x]
v := E[(m-x)^2]

and plot

C · exp(-(m-x)^2/2v)

for the C that makes the quadratic error the smallest and you got yourself a Gaussian fit

https://en.wikipedia.org/wiki/Normality_test

but to be real for a second: normality tests are almost entirely useless. any real-world situation where you might want to perform a normality test, you're either going to find that it's definitely not normal (which is probably an obvious result) or that it's close enough to normal that no one will ever give a shit if you just assume normality

during the biographical parts of my big TOE, did Tom eliminate substances in order to achieve altered states or just to make sure that nothing could fuck with his research?
The way he describes cutting off alcohol, drugs, and food additives is unclear.

when you inhale a strong scent, why does the exhale never have a scent to others?

>>8196491
>never
i am sure never is a strong word, but it's most certainly diminished

there is olphactory neurons in your nose mucosa that actually chemically might break down some of the smell chemicals, also, they probably get stuck around your respiratory path in other ways

>I don't want to turn /sci/ into my personal homework help, but I've been getting confused with the statistics for my dissertation and my supervisor is a fucking idiot qualitative researcher who just shrugs and ignores me whenever I ask him for help, so wondering if anyone could help me out

I used a questionnaire to measure a certain personality construct (X), which can either be conceptualised as a single higher-order construct or five separate facets (X1, X2... X5). My results show low intercorrelations between these facets, so I think it's best to go with them rather than the higher-order construct. Scores for each of these are on a continuous scale between 1 and 7.

I want to see if any of these are associated with performance at two timepoints (Y1, Y2), also measured on a continuous scale. Furthermore, I've also measured the use of two techniques (Z1, Z2), also on a continuous scale. Oh, and just in case it wasn't complicated enough already, I also have a covariate (C) which is likely to have the greatest impact on Y1 and Y2.

Basically, what I want to find out is (a) whether X1, X2, X3, X4 and/or X5 are associated with high performance at Y1 and Y2 (after controlling for C), and (b) whether Z1 and/or Z2 mediate this effect.

(1/2)

>>8196997
However, my data isn't being too kind to me and I'm getting fucking confused trying to work it out. For the first hypothesis, I tried two multiple linear regression models with Y1 or Y2 as the outcome variable, and then having C as my first predictor 'block', then X1, X2, X3, X4 and X5 as additional predictors in the second block. Both times, the ANOVA for the overall model, but none of the individual predictors were significant. Anyone know why this has happened and what I should do next? Should I report it as an insignificant finding, or is it weak but significant? Or have I likely made some mistake somewhere that I need to correct?

I thought maybe I was making it too complicated, so just loaded all of my variables into a correlation matrix to try and understand the data better. This made a bit more sense, and I found some of the expected results (e.g. C was strongly correlated with Y1 and Y2 - Z1 and Z2 were correlated with Y1, Z1 only was correlated with Y2 - X4 and X5 were correlated with Y1, X3 and X5 were correlated with Y2). I now have a general idea of what's going on, but is this enough in terms of statistical analysis? Would I need to do any further tests in order to return to my original hypotheses?

Thanks in advance for any help on this, because I'm really confused and the staff at my university are fucking useless and refuse to help. I'm convinced that there is some easy method to do this, but it goes beyond the scope of what I learned in my stats modules, and at the moment I'm stuck.

(2/2)

Guy who is too retarded to do the math himself here.

Could you use a cannon on the moon to shoot something into orbit?
I suppose the answer is yes. If so, how big does that cannon/gun has to be?
Lets assume a 200kg orbiter here.
Could it get into orbit without additional maneuvers? Could you shoot it in a way, that it will safely return to earth?

>>8197032
No. You can't get it to orbit because any unpropelled object will have a trajectory that passes through to its original location(In a 1 body system). But you can get it to earth I believe.

Anyone know where I could download a PDF copy of Physics in Minutes by Giles Sparrow? I've looked everywhere but can't seem to find it....

>>8197156
buy it

>>8196491
Also, I would say that many (smelly) chemicals will get into your metabolism so extinction will happen with a delay and over a longer period of time. Sulfides (which are what makes rotten eggs smell) are systemic.

What's the point of localization? (Commutative Algebra) What problem motivated the definition?

>>8197032
you could use a cannon that shoots a smaller cannon that puts the object into orbit

>>8196491
fucking vapers

>>8197038
>>8197205
Oh shit. I kind forgot about this problem. But if I shot it from a tower on the biggest mountain of the moon, I'm sure this wouldnt be a problem.
So how much of a gun do I need? Or better: what would be the orbital velocity I would need to archieve in a single impulse?

>>8197235
http://www.1728.org/kepler3a.htm

>>8197168
i wish i could, but i can't order from ebay or amazon, nor can i buy it in my country, so i'm fucked, it's neither expensive nor anything

>>8197251
thanks

Can someone explain to me the meaning of this sentence?

"I don't believe in empirical science. I only believe in a priori truth."

>>8198014
"I am a cunt"
Took me 4 years of grad school to decipher that one, lemme tell ya.

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I've got a wisdom tooth coming in on the top left side of my mouth and it's starting to be a bother. While it was growing in, it didn't really stick out or hurt, but now that it's basically done, I'm feeling some irritation. Is it okay to leave it be, or am I gonna have to get it removed?

>>8198045
Go to a dentist.
He'll probably order an X-ray and later analyze it.
Each case is different. Don't gamble with your health.

>>8198014
Cartesianism.

>>8198063
Okay dad...

I'm not sure how to word this, but I've seen other people make the same observation that I have: math and physics books tend to be written in different styles.

All the math textbooks I've read in undergrad (with the exception of non-rigorous calculus) are very careful about what is an axiom/definition/assumption vs theorem, and how one thing follows from the next. Before throwing out an equation, it is always careful to frame things: "Let G be a group, suppose H is a normal subgroup of G, ... "

On the other hand, physics books (in my limited experience) tend to just throw around equations with lots of variables and integrals over various volumes with little explanation. I'm not saying I don't know what each symbol means, but it can get confusing to follow the logic along, and leaves me feeling a bit more shaky than with math.

Does anyone know of physics books that are written in a style more friendly to math students? Particularly quantum mechanics, but knowing EM and classical mechanics books like this would be good too.

>>8197183
is the wiki page not clear enough? it comes from the geometry but becomes formalized into a universal property

test&*&*(

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>>8198181
I'm not too knowledgeable on this butyou might want to look for books/notes written by people on the math/physics interface, i.e. someone like Peter Woit

http://www.math.columbia.edu/~woit/
http://www.math.columbia.edu/%7Ewoit/QM/qmbook.pdf

>>8198563
>they would probably
Go ask /pol/ faggot. There some cross posters there. But over there they can espouse their political incorrect views.

My professor posed the following question:

"How many integer non-negative solutions are there to x1 + x2 + x3 +
x4 + x5 = 28? what if we assume that all solutions are positive?"

I understand the first question and know that it is C(32,28) or 35,960, but does anyone know what he means by assume all solutions are positive?

>>8198647
he means now you should also exclude zero as a possible value for the x_i to take.

>>8198655
Oh gotcha. I thought maybe that's what he meant, but just wanted to make sure. Thanks

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Is it safe to say that Galois' work that gave the connection between intermediate field extensions L/M/K and subgroups of Gal(L/K) was the first problem solved by looking at it through a sort of different mathematical lens/transferring what is trying to be solved to a very different setting? Kind of hard to word but I hope I'm getting my question across, it just seems like he genuinely had a revolutionary way of thinking

How does carrier mediated transport work to eliminate a drug? In the notes I took I wrote that the process is essentially only active if the drug is a substrate for carriers. I know that's wrong, hit please explain?

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fags on g were too retarded to help me and this is beyond my maths knowledge or interest. However, I need it for a coding project of mine.

let's say a point O with a direction (probably just a unit vector I guess) as a 4x4 matrix. (3 angles and translation vector).
now I have a second vector v that points from O to a point P.
now I rotate O by some arbitrary direction.
if I now multiply v with the rotation Quaternion of O do I get the rotated vector v~?

h-help?

>>8199323
By the way I've never taken any form of class relating to this. I know how the drug is active or passive depending on if it's energized but how does it work to eliminate levels of a drug?

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What method would you use to approach factoring something like a 27 term polynomial of some huge degree?

>>8199564
If it's a one-time thing, I'd look at the graph and start with Newton method at the (27 or less) best guesses

>>8199326
you're a fucktard and you should piss off to /g/.
your question doesnt even make sense and sounds like a lack of understanding some extremely fundamental things.

start reading here https://en.wikipedia.org/wiki/Quaternion

>>8199326
You need to re-phrase your question in coherent English.

>be me
>27 years old
>will be 28 on July 20th
>go to college orientation
>feel out of place
>everyone at orientation was around 17-22
>They all look like fucking children

Man, is this gonna be the longest 2-3 years of my life?

lets assume we know the kinetic energy of a bullet and this bullet impacts a target. The target isnt penetrated and it moves 1,2meters in 1,2 seconds. How can you figure out the mass of the target?.
I was thinking something like using the kinetic energy of the bullet and the speed at what the target moves (1m/s). Is this correct?

>>8199326
Here's what I'm getting from this.

You're trying to say that an object O is set at a particular location and orientation denoted by a 4x4 matrix in the vector space. There is a vector v that points from O to some point P. Now, changing the orientation of O in the vector space, you want to know how, mathematically, the vector v would change from the perspective of the reorienting object O. Right?

>>8200166
2 things missing.

Does the bullet bounce off of the target? Does the target slow to stopping in that 1.2 seconds or does it move at a constant speed after it's been hit?

>>8199953
Your intro classes will suck, higher level stuff will be fun though, especially if you're at a place where the classes get really small.

>>8200166
kinetic energy (KE) = (1/2)mv^2

At what velocity is the target moving initially? That gives you the value of v in the expression for how much KE it had to start with.

At what velocity is the target moving immediately after impact? That gives you the value of v in the expression for how much KE it had after the bullet hit.

The difference between those two is mow much KE is gained from the bullet, which is given to you. After plugging the bullet's KE and the values for v in, you should be left with only one variable, m, which you can solve for using algebra.

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If I traveled faster than the speed of light, would I be running in darkness?

>>8195990
Don't listen to this >>8196114 fucker.
Shapiro-Wilk test it is.

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>>8200229
Faster than light, at least through undistorted space, is a nonsense concept. As you can see from my comprehensive professional totally non-simplified diagram obtained through years of study and research, time moves slower as things move faster. At the spatial speed 0, time moves at its maximum speed. At the spatial speed c, time stops. Any speed faster than c just doesn't exist in the spacetime domain.

saw this earlier
y(y´(x)) = x solve for y

so i assume you would need to find y s.t. y´ = inverse of y. the only function i can really think of that has that property is y(x) = 0. how far off am i?

>>8200308
Serious question here. Is there a consensus about the fundamental principle of the universe? All particles need to be made out of something else in order to exist. Does science believe that this system is infinitely recursive? Is it even possible for a real fundamental particle to exist?

>>8200229
There's a really cool game that's free to download to show you just that

http://gamelab.mit.edu/games/a-slower-speed-of-light/

>>8200281
Wait hold up...

So based off that graph, we can go back in time?

>>8200639
Sure; you just have to go at a negative speed.

>>8195990
So they built a bike which eliminates the caster effect and the gyroscopic effect and it stayed upright, but have they done this in a vacuum?

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How do I find the inverse laplace of the function F(s) shown in the picture?

>>8200769
1. L(

how can people justify having glass platforms and glass stairs, especially in public places like in libraries and with elevations that could kill you if you fell from that height, isn't it dangerous as fuck, like what if a heavy person walks on it or if someone steps too hard on it or if it just breaks from general wear and tear and you fall through it, and it's not just about the safety aspect, isn't it really disrespectful toward people with a fear of heights

like look at how easily the skateboard made of glass breaks at 7:30

https://www.youtube.com/watch?v=KMwhGE0vd-w

>>8200921
or like if someone drops some pointy object on it or walks with stilettos on it

>>8198045
Dentist here.
You have a chance of developing something called pericoronitis that hurts a lot.
It is advised to remove the tooth before this in order to avoid pain and complications.
The procedure is simple.

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>>8200921
ok they seem to have wooden stairs, but i could have sworn they used to have glass stairs

>>8199953
You wont be the only oldfag there i can tell you that much.
Eventually you will find people that are falling behind or old as you and life will pick up from there.
The important thing is to remember that nobody gives a shit about anyone.
Dont be nervous because nobody cares.

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>>8200936
they actually did/do have glass stairs, this pic looks weird since it doesn't look transparent/translucent (maybe they painted it or something because it freaked people out) but it does say it's a glass stair and glass floor

>>8199953
age shouldn't be a problem at all

>>8200944
>read did/do as dildo

Was disappointed when I realized my mistake.

>>8200921
>>8200921
http://www.bbc.co.uk/news/technology-36494150
Stop being a pussssssyyyy.

>>8201000
> this one didn't break so none of it will break
anal kek

>>8201000
>Panicked tourists stampede across bridge as 3000ft-high glass walkway shatters beneath their feet

>But last September, tourists on a different walkway in China panicked when a panel smashed. A visitor had dropped a mug. The walkway had to be closed for repairs.

dude...

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>>8200921
>isn't it really disrespectful
muh male/thin/non-acrophobia privileges
10/10 you made me slightly upset

>>8201018
thats actually a nice tresher for the fat people. the mighty glass will decide if you're thin enough to deserve to live or simply die in a terrifying fatass way :^)

>>8201024
you are a pure genius anon, why didnt i think of this

>>8201018
a public place funded by taxpayer money like a library should be accessible to everyone (within reason), and glass stairs and platforms is a bit ridiculous, probably costs a lot for maintenance and repairs, you have to clean the glass and check for structural damage, and it's not even all that cool in the first place, they're just fucking stairs, they should just be there to walk on, not for architecture fetishists to fap to or for creeps to take upskirt photos through the glass

>>8201048
i dont think they take much more maintenance than normal, but dont quote me on that. thought i do agree with the last two points.
just to make it clear, i couldnt care what they made their stuff out of as long as its structurally sound, but glass would almost never be my first material of choice for that purpose, it has its places though

Could anybody give me general study tips and advice? Specifically, I need to study and refresh myself on a lot of material before starting grad school next month.

For Statistics, I'm not sure how to approach it since I'm awful at maths and I would imagine studying maths is entirely different than anything not-maths or physics (since no equations/problems, that sort of thing.)

Otherwise, for strictly information memorization, I was going to read a certain amount every day, try to pay attention to specific important information, make flash cards to help with memorizing and retaining key terms, and I'm not sure where to go beyond there.

My chemistry teacher was telling me some shit today but I wasn't paying attention and I don't enough to google it. All I can remember is that random molecules in something do some magnetic polar shit and it causes them to all line up or attract. THe signifact fact is that its random, but on a macroscopic scale its a reliable behaviour.

>>8202016
Sounds cool. Maybe your textbook will say something about it.

>>8202020

Don't have one. I'm English, we don't need pay $80 for the latest version that contains no new information. This is a stupid questions thread, so there's no point in being salty and passive aggressive about it.

>>8202058
is this what you're looking for?

https://www.google.com/#q=random+molecules+in+something+do+some+polar+shit+and+it+causes+them+to+all+line+up+or+attract

>>8202078

>everything from capacitors to hyrdogen bonding, which I know about so why the fuck would she repeat herself

This is why you were bullied in school. Its some brownian motion shit.

>>8202085
the first result

http://chemistry.stackexchange.com/questions/1289/how-do-non-polar-substances-dissolve-in-non-polar-solvents

is this not it?

>>8202120

Yeah yeah, that's it, the electrons. Sorry man, obviously when I was googling first time I didn't type that.

>>8202127
kek it's all good have fun

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>>8202131

Thanks. Have a Sunday Sport article.

>>8198181
>On the other hand, physics books (in my limited experience) tend to just throw around equations with lots of variables and integrals over various volumes with little explanation. I'm not saying I don't know what each symbol means, but it can get confusing to follow the logic along, and leaves me feeling a bit more shaky than with math.

sounds like the pretension version of "hold my hand these big equations are scary looking". don't kid yourself. the reason you have trouble with the equations with "lots of variables" is not because it isn't rigorous (it isn't), but because you don't understand the equations.

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Are these talking about the same thing? Where does the value of the underlined term come from?

>>8200817
Thanks man

This will sound stupid, but worth asking.
What are the legalities and challenges in building private, unmanned, interplanetary research craft?
Such as a rover/robot that could act as a remote lab on say, venus or mars.

>>8202841
Hi, Elon.

>>8202864
Not elon, just a lurker.

>>8202841
transportation would be the main challenge. unless you're filthy rich or you get funded somehow it's not gonna happen any time soon

>>8195990
you can tell it's normal because of the way that it is

>>8200762
this bicycle research seems pretty dim-witted, hap-hazard and primitive
>https://en.wikipedia.org/wiki/Two-mass-skate_bicycle
>The existence of the TMS and the self-stability it exhibits suggests that the design envelope of rideable bikes is larger than previously thought.[7][8][9] For example, rear-wheel steering may not be as impossible as has been claimed.
>rear-wheel steering may not be as impossible as has been claimed
no shit sherlock!

>>8202841
Money.
Cheapest rocker costs 5 mil in one way and only gets you to the moon.

>>8203040
Rocket*

Anyone here know shit about vector fields

>>8203066
Likely.

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Lets say I have a regular field storing normalized(length 1) vectors of a vector field(imagine pic-related but all the 2d vectors are of length 1).
I can access this 2d field by integer xy coordinates to pick a vector. I need a way to trace the approximate shape using only these values. If you were to logically pick one vector and follow it to the next sampled vector you would trace a pixelated circle right?
I need a way to traverse this graph to recreate the path of this "circle".

Function for this vectorfield is (-y,x)

>>8203083
Should I just pick a point, get the "next" pixel and add the current direction vector to this one and basically just accumulate all the vectors following this path? It's basically contouring but only with these finite points

>>8203083
In general, the path whose tangent at each point is parallel to the field direction won't be a closed loop. If the field is continuous, then a path can't self-intersect, but it may be an infinite spiral.

The only situation where it will be a closed loop is if the vector field is constructed by finding the gradient of a potential field then taking the normalised perpendicular vector at each point.

If the vector field has been quantised, then any attempt to construct the path probably won't form a closed loop simply due to quantisation errors.

I suspect that your best bet will be to rotate the vectors so that they form a gradient field (effectively a normal map), generate a potential field via deconvolution, then trace contours of constant potential (which are guaranteed to be closed loops).

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>>8203100
The thing about this situation is that I have a lot of criteria for a "bail out". So after it traverses a certain amount of steps it will give up. Or if it hits another criteria(these points aren't just storing directional vectors but other data).
Is adding up the tangents the right way though?

Lets say this field for example. They all have the same slope.(0.42i + 0.3j ; Random vector, not normalized)

I want go from one point to another with the smallest amount of "error". Using just these slopes I basically attempt to recreate the contour to create a "raster" path jumping from one node to another.

This is similar to this algorithm in how it decides when it should move to the next row/column by finding the path with the least error based on the raster shape(which goes well "between" the pixel points)
https://www.cs.helsinki.fi/group/goa/mallinnus/lines/bresenh.html

Lets say for example I want to create a pixel-image contour. You pick any point on this field and iterate lets say exactly 100 pixels(100 node-jumps) from this point and you then get a contour path from this one point. Would adding up all the slopes from this one starting point be enough to do this?
What if the path was circular like the original image?

>>8203109
I also notice that the circular variation of this algorithm uses 2*x and 2*y which look like derivatives of x^2 and y^2.
https://en.wikipedia.org/wiki/Midpoint_circle_algorithm#C_Example
and it seems to constantly add this variable(plus 1?) to this error variable.

It's almost integrating and adding up all the tangents from one point to another to re-create the actual shape but if the slopes I have are only at a regular finite resolution would it still be enough to recreate this shape?

How do I learn to stick to studying?
I do it for one hour, then I stop the next days.

I really want to learn, yet I suffer greatly from a lack of motivation, additionally I have a big apathy going on and never really manage to sleep right on time...

What do?

>>8203109
The vectors are the derivatives of a curve. You're trying to reconstruct the curve by integrating the derivatives.

Like anything involving numerical integration, errors will accumulate, so if you try to follow a closed loop, when you get back to the starting point you'll be off to one side or the other by some amount.

You'll get better results if your coordinates aren't restricted to integers and you calculate the direction at any given point by interpolating the nearest vectors.

None of this has anything to do with line-drawing or circle-drawing algorithms.

>>8203135
If you think one hour per day is enough studying then you have bigger problems.
Depending on the uni it simply wont cut it.

>>8203145
I know.
I want to study 4 hours a day or up to 8.
How do I reach that goal without tapping out?

I cant for the life of me seem to work this out even though it should be simple

If R and S are matrices of the same size, solve the following equation for T:
2(R+S+T)-(2R-3S+T)+3(S-T) = O (the letter o, not zero)

i know i can expand it to, 2R+2S+2T-2R-3S+T+3S-3T = O

and im left with 2S = O, but from there i cant seem to figure out what T equals. the answer say T = 4S but i cant get there no matter what i switch around and what not

>>8203178
> 2(R+S+T)-(2R-3S+T)+3(S-T) = O (the letter o, not zero)
> i know i can expand it to
> 2R+2S+2T-2R-3S+T+3S-3T = O
That's wrong. It should be
2R+2S+2T-2R+3S-T+3S-3T = O
Note the signs of the first 3S term and the T terms. You only negated the first term inside the second set of parentheses rather than all 3.

That reduces to 8S-2T=O => 2T=8S-O => T=4S-O/2.

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>>8203216
ohhh i see, as dumb as it is, negatives still throw me out like fuck sometimes

thank you very much!

>>8202658
It's just a different notation and normalization. In the first case e_n is defined without the square root factor, whereas the second case defines e_n with an additional square root of 2pi. That's where the square root of 2pi difference comes.

It's usually always like this btw, with Fourier series: you need some factors of 2pi to be somewhere, so you decide where you wanna hide them, but they'll appear somewhere.

>>8201407
Please respond.

>>8203150
you just have to get into a studying habit, try to really force yourself into starting and then you'll naturally keep going for a while, but of course you can take breaks, like study for 1-2 hours and eat a meal or drink some coffee or whatever it is that you want to do. during the breaks and whenever you're not studying your brain will process the information more or less automatically but you need to do the initial studying so that your brain has something to process.

>>8202872
>>8203040
would it be worthwhile then to pitch the idea to an agency or business in exchange for being able to use a small portion of the project for my own research?

how exactly did tesla plan to generate wireless electricity without killing everyone inside the effective field?

>>8203651
pitch it on shark tank

>>8203651
I dont know if you are aware of this but there is a huge program going on right now sponsored by google.
Tons of universities and students participate from all around the world some of them offer spare research cargo space for cheap.
I dont know how you missed this like everyone is on it.

>http://lunar.xprize.org/
There are tons of talks about this on CCC,Defcon ect. you can find them on youtube.

>>8203667
My interest in space travel is fairly recent.
My normal projects are mostly in robotics.
Thanks for the info though, this really helps.

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What would happen if you kept cutting a square like this? Would it divide infinitely?

>>8204114
yes

>>8204168
But can you physically do that? Wouldn't matter eventually run out or something if you hypothetically kept going smaller?

How do I become a top student?

Going into a physics undergrad program soon.

Anyone know this?
>>8204022

>>8204174
The concept of "cutting" only makes sense on a macroscopic scale. Go small enough and it loses all meaning; the question becomes nonsensical. Elementary particles are probably as deep as you can go without losing the meaning.

>>8204174
>implying a square is a physical object

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>>8204280
>implying you can only cut physical objects

>>8196997
>fucking idiot qualitative researcher
>Lol, subjective information is irrelevant, I'm just going to ask people what they think but reduce this information to a bunch of data points so that I can imagine it as being objective because muh science

>>8204202
Use your summers to study ahead
Pomodoro
Set dedicated hours in the day to focused studying
Get enough sleep

>>8195990
when there are events be it political or other photographers use tricks like taking pictures really close to the people but a little high to make it seem like hundreds of people are thousands, is there a way to calculate the real amount of people in one of these pictures?

I want to prepare for grad school next year. I'm a bachelor in CS (pls no bully). I have a solid idea of what topics to study but I have some questions.

1. Should I study one book at a time? I've tried covering 3 different subjects at the time, study subject A: Mon, Wed, Fri - Subject B Tue - Thu. Subject C - Sat (longer than week days sessions). I feel I'm advancing slowly. Should I study one topic at a time?

2. I want to get into the habit of reading papers related to mathematics and CS. What's a good resource to start?

>>8204225
I see, thank you.

>>8204202
be born non-retarded

is something multiplied by 0 in a matrix NOT equal to zero? this is what my worksheet answer is

[math]
I=\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}, A=\begin{bmatrix}1 & 0 \\ 2 & 3\end{bmatrix}
[/math]
[math]
IA = \begin{bmatrix} 1 & 0 \\ 2 & 3\end{bmatrix}
[/math]

>>8204834
Matrix multiplication isn't element wise.

If C=A*B, then c[i,j] = sum[k](a[i,k]*b[k,j]).

It /isn't/ c[i,j]=a[i,j]*b[i,j]

>>8204834
You multiply rows on the left by columns on the right, and the result goes where the overlap was, if that makes any sense
e.g.

[ 1 0 ] [ a b ]
[ 0 1 ] [ c d ]

rows: top (1, 0), bottom (0, 1)
columns: left (a,c), right (b, d)

top left: (1,0) . (a,c) = 1a + 0c = a
top right: (1,0) . (b,d) = 1b + 0d = b
bottom left: (0,1) . (a,c) = 0a + 1c = c
bottom right: (0,1) . (b,d) = 0b + 1d = d

[ 1 0 ] [ a b ] -- [ a b ]
[ 0 1 ] [ c d ] -- [ c d ]

>>8204344
The fucking idiot and qualitative researcher were separate - he can't help because he is (a) a fucking idiot who thrives on being unhelpful, and (b) a qualitative researcher who has limited experience with quantitative research. I agree that qualitative research is a useful tool when used in conjunction with quantitative research, but a lot of is incredibly shit-tier (including my supervisor's). That said, lots of quantitative research in psychology is shit-tier too.

STATS GODS I NEED YOU

I ran an experiment with two conditions (T1 and T2), where performance was the outcome variable. I want to assess whether 3 particular predictors (P1, P2, P3) are associated with performance.

First set of analyses I looked at T1 and T2 separately. At T1, P1 and P2 were positively associated with performance, and P3 was negatively associated with performance. At T2, P1 and P3 were no longer significant, and P2 was still significant. That's all fine, and interesting to me in terms of my original predictions.

However, at T1 and T2 there's a covariate (previous experience) which affects performance and muddies the data a bit. So I decided to create a new outcome variable measuring change in performance - thus nullifying the covariate, seeing as each participant's score is measured against themselves. But here's where the data starts to get fucked up - when I look at the correlations now, P1 and P2 are negatively related with change in performance, and P3 is positively related with change in performance. In other words, the first set of analyses tell me that P1 and P2 help performance whereas P3 hinders it, and the second analysis tells me that P1 and P2 are bad for performance and P3 is good for it.

Can anyone explain why this has happened? I've already checked to make sure that I computed the 'performance change' variable the right way.

>>8205028
> P1 and P2 are negatively related with change in performance, and P3 is positively related with change in performance.
If the relationship between performance and predictors Pi is genuinely linear (an assumption that you make implicitly whenever you look at correlation) then the change in performance with respect to a change in Pi should be zero by definition.

Are the results of your second analysis significant? If not, you might be a victim of multicollinearity (wiki it), and in that case I'd suggest discarding your second analysis and simply including the experience covariate as a fourth 'predictor' when you conduct the regression.

Why does my matcha bowl (ceramic) emit noises when i pour boiled water in it? It sounds like crickets/wildlife on a nature recording.

Also is DEET + window nets + full body cover a good mosquito deterrent?

>>8204849
>>8204931
oh i see thanks, for some reason my worksheet showed me matrixes like

[math]\begin{bmatrix}
a & b & c
\end{bmatrix} \times
\begin{bmatrix}z
\\ x
\\ y

\end{bmatrix}
[/math]

but not equal ones

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How did the different primitive peoples of the world start fires?

>>8205125
The relationships I mentioned were all from a correlation matrix, but I also tested each one individually using linear regression and the same relationships (i.e. significant or non-significant) were found.

I've tried putting them all in a multiple linear regression model, with the covariate in the first block and the significant predictors in the next block - when I do this, the ANOVA for the model is highly significant (P<0.0005) but none of the predictors are significant. I have no idea why that is happening, could you explain it? There is some evidence of multicollinearity, but nothing straightforward (P1 isn't correlated with the covariate but P2 and P3 are, P1 is correlated with P2 but not P3, and P2 and P3 are correlated with each other). How the fuck do I write up those results?

>>8205163
combustion.

>>8205134

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the answer is actually
t = (2L0/mg (M + 3m) )^1/2

where the heck does the 3 come from?

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>>8205182
also my answer for this question is double what it should be...

>>8205172
I should add that, although the predictors had various intercorrelations, when I ran the collinearity diagnostics on my regression, the VIF for each predictor was at very acceptable levels (between 1 and 2.5).

>>8198014
An a priori truth is something you can deduce. Empirical science is something you observe.

I think this link might be relevant.
http://plato.stanford.edu/entries/descartes-epistemology/#3.2

What kind of problem is this:
You have n items, each of different weight, and you need to pack them all in knapsacks, but you need to sort them out so you use the minimal number of backpacks. And each knapsack can hold the same weight W.

It's similar to the knapsack problem, but in the knapsack problem, you have n items and 1 knapsack and you need to choose the most valuable set of items to pack inside.

Is this something already done somewhere?

>>8205203
Bin-packing problem.

>>8205207
thank you

if you plant stem cells from another species somewhere in your body do they turn into human cells?

>be watching Cube on youtube

>a character (a math student) realizes that rooms marked with prime numbers mean danger

>The numbers are represented as everyday strings of base-ten numerals

>the character stares at a three-digit number ending in 5

>one-mississippi, two-mississippi, the character is deep in thought

>"No, that number is not prime"

>>8205854
>tfw no sieve

I have been on a ton of different pills all my life from 8 to the beginning of this year (23) and I couldn't possibly tell you all I took because nobody knows, it caused me tons of secondary effects like obesity and memory loss. I have such an awful memory I can forget things as I'm doing them, I retain nothing and such. Is there any way to revert this? Any solution? Is it even worth it to live another 50 years like this?

>>8205854
>watch retarded show
>get annoyed when characters act retarded
are you retarded?

Why are the most notable irrational numbers so small? e, pi, phi, Euler's consant, i^i, they are all pretty small. Do larger numbers like 16.39845983... and 100010010.10100100010000... have just as much significance, and we are just small number centric?

>>8206697
I suppose because

> we haven't found as many significant large digit numbers yet, possibly because they're slower to calculate/compute
> big numbers come from small numbers, naturals for instance can be defined as N = [ 0 | N + 1 ] so simpler numbers correspond to simpler (and more general) laws
> a lot of significant numbers correspond to geometry or physics, most of what we can study there has been on a human level - but we've since discovered much larger things like avogadro's constant (6x10^23 or something)

>>8206697
Two and three come up more often and tend to behave much differently from larger integers, providing frequent counterexamples. It's just a small numbers thing.

>>8204834
I'm going to take a second here to try and illuminate the concept of matrix multiplication. The key point to keep in mind is that given a basis on the source and target, a matrix is supposed to encode all of the information of a linear transformation. Let [math]T:V \to W[/math] be a linear transformation, and choose bases [math]v_1,\dotsc,v_n[/math] and [math]w_1,\dotsc,w_m[/math] for V and W, resp. The first column of our matrix corresponding to T is the coordinates of [math]T(v_1)[/math] with respect to the [math]w_i[/math]-basis. In general, the [math]i[/math]-th column is given by the coordinates for [math]T(v_i)[/math]. Now, matrix multiplication is nothing but a composition of the underlying functions, and you can chase basis vectors around to convince yourself of the formula for matrix multiplication.

>>8206697
I’m also a man of science. Of numbers. The way I move through space with minimum waste and maximum joy is all about mathematical probabilities. I look at things happening around me and try to extrapolate what they will be like in the future. I seek patterns in the numbers, and what I see ain’t pretty.

I am trying to find the radius of convergence for [math] \sum_{0}^{\infty} n^{p}c_{n}z^{n} [/math] given that
[math] \sum_{0}^{\infty}c_{n}z^{n} [/math] has radius of convergence [math]R[/math].
I wanna use the Cauchy Hadamard Formula since that's all they use in the book. The answer is [math]R[/math]

>>8196148
>but to be real for a second: normality tests are almost entirely useless.

Indeed. I was researching this a few years ago because I needed to 'blindly' (i.e. automatically) check a few hundred distributions for their normality. After trying with basically every statistical test one could find in the usual software modules, I gave up. Talked to quite a few senior scientists, they all just recommended me to fit a Gaussian distribution to the data, and check visually if they match up or not.

Most statistical tests are just too feeble w.r.t outliers, sample size, yadda yadda.

>>8206943
I figured it out. Ignore this post.

>>8206952
Does that include the Shapiro-Wilk and Kolmogorov-Smirnov tests? Those are the ones we use in psychology (depending on sample size), which then helps determine whether or not to run a parametric or non-parametric test. But if visual analysis is better, it'd probably be easier just to do that.

Why do highschool science teachers have an inflated view of the importance of their field?

Allegedly, R^3 minus two linked circles is homotopy equivalent to S^2 wedged with a torus. Is there an easy way to see this deformation? I've heard that thinking of R^3 as living in S^3 instead is helpful, but I still don't see it.

>>8207352
because it's all they know

How do I evaluate the expression using binomial coefficients? I'm pretty lost about how to do this for my online class.

1^3 + 2^3 +.... +n^3

Any help appreciated

>>8195990
You can tell it's not normal distribution just by eyeballing it.

>>8207481
> How do I evaluate the expression using binomial coefficients?
> 1^3 + 2^3 +.... +n^3

If S(n) is the sum to n terms, then

S(1) = 1
S(n+1)-S(n)=(n+1)^3

If f(n)=c*n^k+... (i.e. a polynomial of degree k with leading coefficient c), then f(n+1)=c*(n+1)^k+... = c*n^k+... (also a polynomial of degree k with leading coefficient c), so f(n+1)-f(n) will have degree k-1 (the c*n^k terms cancel).

So the sum of a series of cubes will be a polynomial of degree 4.

Put S(n)=c4*x^4+c3*x^3+c2*x^2+c1*x+c0, and expand out S(n+1)-S(n)=(n+1)^3. Equating terms will give you a system of linear equations in c1..c4 (c0 cancels). Adding S(1)=1 gives you a term involving c0. Solving gives
S(n)=(n^2+2*n^3+n^4)/4. = n^2*(n^2+2*n+1)/4 = n^2*(n+1)^2/4.

This is goddamn basic algebra and it's making me feel stupid because I forgot this. I hate it when people go to 4chan to get people to solve their problems but this is exactly what I'm about to do.

After solving most of a problem about reactor design I've ended up with the equation [math]x/(1-x) = -ln(x)[/math] with X being the conversion of a reagent in percentage. Because of this I know that the range of the solution will be 0 < x < 1.

I am completely unable to get such an equation down to a form such as [math]x = C[/math] with C being a number.
I'm only able to solve it by arranging the equation as[math]x/(1-x) + ln(x)= 0[/math] and guessing values of x until I get the result closest to 0 with 3 significant digits.

However this is too time-consuming, how do change that equation to [math]x = C[/math]?

I simply cant understand, why this it true?
" -(a-b)=b-a

>>8202897
thats pretty neat

>>8207691
-(a-b)
(-1)(a-b)
((-1)a - (-1)b)
(-a + b)
(b - a)

>>8207709
Thanks for helping to retard

Having trouble finding the derivative function of [math] f^1(x)=\lim_{h \to 0} \frac{f(x+h)+h)}{h}[/math]

Where [math]f(x)=\frac{1}{3}x^3-x

I have to show my work so I can't use that exponent shortcut.

>>8208235
Numerator should've been +f(x) on the left side.

next line was supposed to say (1/3)x^3-x

I know it comes out to x^2 but I can't get passed the algebra

>>8208235
>>8208239
lol Americans...

>>8208235
Have you tried literally plugging the function you are given into the limit?

>>8207653
You need to solve numerically, e.g. using Newton's method. Which gives x=0.446432978437.

Why aren't genetic factors given more consideration when attempting to explain behaviour?

>>8208552
because globalist jews run the world and people aren't allowed to be "racist"

what is the square root of pi?

>>8208623
[math]\sqrt{\pi}[/math]

>>8208552
Behaviourism, as a school of psychology, really took off in the second half of the 20th century, as a new explanation of human behaviour. Remember, before then, all human behaviour was thought to be the result of innate causes. The new behaviourist school was politically/socially appealing because it allowed for a much greater attribution of environmental causes to behaviour, and, consequently, the potential to improve undesired human behaviour. It fits into lots of 'progressive' ideologies like feminism. Furthermore, it seemed to check out scientifically too, which is why quite a lot of psychology departments are quite radically behaviourist and ignore biological explanations. However, there has been a backlash in recent years and many behaviours and conditions are thought to have epigenetic (environment x genetic interaction) causes. Steven Pinker's The Blank Slate is a pretty interesting book on this topic, if you've not already read it.

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How do I fix this?

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Okay, stupid question here...
Cold fusion, yeah? Listen... that name was coined by the man who got his peers vote to dismiss it named it so in jest.
Is this thing called "Cold Fusion" a real thing? I mean, are there people on earth that use it?

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Wew, never mind. It was just the previewer acting up. All I had to do was refresh the page.

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Is this correct in any way, shape or form?
My script says that the electrostatic potential energy of q is the energy required to move it from its current distance to the charge that builds up the field to infinity (or negative and the other way around).
For a point charge like an electron thats what I did here, but it just looks wrong for some reason.
Can anyone reassure me or tell me how its wrong?

[math] Theorem: Suppose \sum_{n=0}^{\infty}C_{n}z^{n} is zero at all points of a nonzero sequence {z_{k}} which converges to zero. Then the power series if identically zero. [/math]

[math]
Corollary: If a power series equals zero at all the points of a set with an accumulation point at the origin, the power series is identically zero. [/math]

Now the question is to prove this corollary by showing that if a set S has an accumulation point at 0, it contains a sequence of non-zero terms that converges to 0.

Is it valid to argue that suppose there is only a sequence of terms all zero that converge to zero and if that is the case then the set S has an isolated point at 0, contradiction. I know other ways to argue this simple fact but was just wondering if this was actually valid.

>>8209244
Wow fuck me.

Theore: Suppose [math]\sum_{n=0}^{\infty} [/math] is zero at all points of a nonzero sequence [math] {z_{k}} which converges to zero. Then the power series if identically zero.

Corollay: If a power series equals zero at all the points of a set with an accumulation point at the origin, the power series if identically zero.

>>8209244
>>8209250
Last try

Theorem: Suppose [math]\sum_{n=0}^{\infty}C_{n}z^{n} [/math] is zero at all points of a nonzero sequence [math]{z_{k}} [/math] which converges to zero. Then the power series is identically zero.

Corollary: If a power series equals zero at all points of a set with an accumulation point at the origin, the power series is identically zero.

how can i proof

m^(n+1)=m(m^n)

Makes perfect logical sense that if m^n is really mmmmmm.... n times, then m^(n+1) just adds another m to the string. Be as rigorous as you can please

>>8209299
> how can i proof
> m^(n+1)=m(m^n)
You can't "prove" it; that's literally the definition of ^. Well, that and m^0=1.

>>8209390
Thats the definition for naturals.
The definition for reals is given by [eqn] a ^ x := \exp ( x \ln a ) [/eqn].

Does anyone have a good set of notes on adjoints that goes into how they tend to be used in practice? Categories for the Working Mathematician has you prove a couple simple of functors are adjoint, but that's it.

>>8209458
They're a generalization of adjoint operators in linear algebra, no?

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I dont get it then. I can equalize the same thing for addition and multiplication:

>m+(n+1) = (m+n)+1
m+n+1 = m+n+1
Easy peasy, i wont show the whole proof (im using the rational number field)

>m(n+1) = (mn)+m
(mn+m) = (mn)+m
mn+m = mn+m
A couple more steps, still easy af

>m^(n+1) = (m^n)m
?????
Please tell me why i cant simplify this in the same way. Or rather, why wouldnt it be verifiable

I should mention i am following wildberger's foundations of math series (or maybe i shouldnt)

>>8209502
[math](m^n)^m[/math] by properties of exponents makes the expression equivalent to [math]m^{n \cdot m}[/math]

>>8209502
Wildberger doesn't define fractional powers
If you restrict it to natural powers your expression is an axiom.
If you don't you have to define powers some way. Check proofwiki for definitions for different number systems

>>8209468
They both involve saying (Ax,y) = (x, By) in some way (that pair could be Hom sets or inner products).

>>8205137
Those matrices are vectors then.
[eqn]
\begin{aligned}
\mathbf{A} &= \begin{bmatrix}
a & b & c
\end{bmatrix} \\
\mathbf{B} &= \begin{bmatrix}
x \\ y \\ z
\end{bmatrix}
\end{aligned}
[/eqn]
[math]\mathbf{A}[/math] is a three-dimensional row vector (1 x 3 matrix) whereas [math]\mathbf{B}[/math] is a three-dimensional column vector (3 x 1 matrix). In general, 1 x m is a row vector whereas n x 1 is a column vector.

>>8209502
> Please tell me why i cant simplify this in the same way. Or rather, why wouldnt it be verifiable
Oh, it's verifiable. But the proof has zero steps; you're stating an axiom.

"Proving" that m^(n+1)=m*(m^n) is like proving that n+0=n or that i is the square root of -1.

>>8209583
is m^(n+1) defined as m(m^n) or (m^n)m

I got a dumb question

If [math] f [/math] is differentiable on [math] I [/math], the derivative [math] f' [/math] is obviously Riemann integrable, right?

>>8209801
a function from R to R? in this case, this is the fundamental theorem of calculus, which isn't "obvious"

If X is a Scheme, then in what cases is Aut(X) also a Scheme?

>>8209801
Every bounded continuous function is Riemann integrable.

>>8209841
a derivative doesn't need to be continuous...

>>8209845
I misread his post.

>>8209813
Wikipedia adds a "If f' is riemann integrable" clause in the second fundamental theorem of calculus formal definition
And Tao keeps adding it to later proofs (Thm 11.10.2 in the "Consequences of the fundamental theorems" section)
And my proof is in some notes that aren't with me.

>>8208543
I actually don't remember ever learning this method in my country.
Thank you very much.

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Just out of curiosity (and since I don't want to make a new thread for this) how much extra-curricular studying do you guys do in your free time? Like how many hours per week do you spend studying subjects outside your major/work field?

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I'm fucking stuck on precalc/basic algebra showing up in learning stuff.

sorry for retardation but how exactly does one invert the relation to be phi in terms of eta?

Does anyone know of a source that discusses the effect of mean shifting on entropy (information theory)?

>>8210041
[math]
$ \eta = \log{\frac{\phi}{1 - \phi}} $ \\
$ e^\eta = \frac{\phi}{1 - \phi} $ \\
$ e^{-\eta} = \frac{1-\phi}{\phi} $ \\
$ e^{-\eta} = \frac{1}{\phi} - \frac{\phi}{\phi} $ \\
$ e^{-\eta} = \frac{1}{\phi} - 1 $ \\
$ e^{-\eta} + 1= \frac{1}{\phi} $ \\
$ \frac{1}{e^{-\eta} + 1}= \phi $ \\
[/math]

>>8209592
Depending on which formalization you're using. You can define it either way and still be consistent. It's usually the first one.

>>8210051
fuck me, much appreciated anon

>>8210077
Sometimes it's easier to work backwards. Note that there's only one instance of [math]\eta[/math] in the second equation, so it's a bit easier to isolate. Then just do the steps in reverse order.

>>8210083
yeah, im rusty as hell with logs and probability functions

Why do macro organisms have to sleep but not micro organisms when our cells do essentially the same work?

>>8210102
Cells can only use so much energy and perform so much work in a set amount of time. The complexity of macro organisms requires a pretty high demand of cellular activity, which can be made up for by a) having a fairly large cellular volume (which becomes inefficient/counter-intuitive due to the increase in mass creating more energy demands) or b) reducing the energy expenditure of the macro through extended periods to allow the cells to catch up.

Or at least that's my understanding. May be incorrect

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So I'm doing a adult math program to get into a course. I got the following question:

Lauren wants to fill her pond with water. Her pond is in the shape of a rectangular prism with a length of 4m, width of 3m, and depth of 1.5m. If it costs $2.5 per cubic meter for water, how much would it cost?

So I got 1.5 x 4 x 3 = 18m3 x 2.5 = $45.

The answer key in the back reads:
18 x 2.25 = $40.5

Am I retarded or is the book wrong?

>>8210341
>it costs $2.5 per cubic meter for water
>The answer key in the back reads: 18 x 2.25 = $40.5
Everything you did is right. Either the book has a misprint or you may have read a wrong value.

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>>8210358
>>8210341
This is not the first time this book has thrown me off.

>>8210361
So apparently the cost was supposed to be $2.25, not $2.5.

integrating tanx*sec^2x

I can set u = tanx, du = sec^2x
and get tan^2x/2

Or I can make the integral tanx*secx*secx

And set u = secx, du = secx*tanx
And get sec^2x/2

Right? Are both answers correct? If so, how?

>>8210648
You're forgetting the [math]+C[/math]s. Never forget the [math]+C[/math]s. Consider the Pythogorean trig identity

[math]sin^2x + cos^2x = 1[/math]

(divide by [math]cos^2x[/math])

[math]tan^2x + 1 = sec^2x[/math]

Thus, it is true that [math]tan^2x + C_1 = sec^2x + C_2[/math] for some [math]C_1, C_2[/math].

>>8210662
That makes sense. Thanks a lot.

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>>8210710
It's not like people just have that memorized, by the way. I'm guessing you didn't know what [math]tan^2x, sec^2x[/math] actually looked like. Which is okay, but now we have graphing calculators.

Graphing almost always helps understand a problem. Math isn't just about pushing symbols around. Try to understand what the symbols are saying.

>>8210722
Very helpful. Your previous post also inspired me to learn how to actually derive the trig identities. It always looked more complicated than I now think it actually is. This is the first time I've ever asked a math question, including in class, and it helped me a lot. I'm going to start asking more questions now. You may have just changed my life, dude. Thanks again.

>>8210742
Cheers anon. Questions are good. Office hours are good, if you're in college (or if not, just asking the teacher after class). Professors also tend to give away hints about the exam questions at office hours, for extra motivation.

How do I find the limit of

[eqn]\lim_{n\to\infty} \frac{a^n}{b^n}[/eqn]

>>8210883
For starters, you first have to understand that
[eqn]\lim_{n\to\infty} \frac{a^n}{b^n} = \lim_{n\to\infty} \left( \frac{a}{b} \right)^n[/eqn]

>>8201407
If you have math problems that you missed, look back at it and figure out why you missed it.
When you find out, retry the problem until you get it right.

After, write down why you missed it and write down a tip like "remember to do X" or "Simplify Y" etc.

You don't need to remember what you wrote down because it should come back when you see a similar question

idk its what i did way back in high skool

would figuring out a way to remove excess adenosine from your body eliminate the need for sleep?

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Is this a trick question?

i cant get it to = 0, i even used a calculator online and it didnt equal 0

also it cant be a trick question so somthing is messed up

>>8211041
>and it didnt equal 0
Well what does it equal, then?

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>>8211041
>>8211055 here, I think I found the problem.

>>8211055
well the online calculator says [math]\begin{bmatrix} -6 & 0 \\ 18 & 24\end{bmatrix}[/math]

worksheet says nothing because the answer is supposed to be 0

>>8211062
Yeah, something messed up.

It's either supposed to be [math]B^2 - 3B - 4I = 0[/math] or the matrix is supposed to be [math]-B[/math] and not [math]B[/math] or something, if that even makes sense. Either way, something's wrong.

>>8211072
ty! ill email the professors sometime

>>8211041
>[math]=O[/math]
Top lel

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>>8211072
Oh yeah, the next question actually says it is -3B, guess they made a typo

>>8211088
Well there you have it.

Might have to do something about the O as well. I don't think most people use O to represent zero matrices.

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>>8211100
thanks for your help anon ^-^

>>8210039
I would say 90% of the time I spend on learning things that are not in my domain of work.
I lost any and all love for what I do.

Hey, I'm another /g/ babby. The only part of maths in school or uni that I just could not bring myself to be interested in is statistical analysis. I have some understanding of the concepts but the formulae just seem alien and different compared to everything else I know and my brain just shuts off.

Here's what I need:
I have a greyscale image represented by a H x W matrix with values in the range [0 .. 255]. I need to calculate the standard deviation of the pixel values.
I've looked around and found this formula (let's see if my Latex is still good):

[math]\sigma = \sqrt{\sigma^2}[/math]
[math]\sigma^2 = \sum \limits_{i \in [0, 255]} (x_i - \mu)^2 \cdot P(X=x_i)[/math]

Assuming all values are equally probable: [math]\mu = 127[/math].
The probability of a value occuring is [math]P(X = x_i) = {count(x_i) \over {H cdot W}}[/math] where [math]count(x_i)[/math] is just how often the value [math]x_i[/math] occurs in the image.

So I would end up with this formula:
[math]\sigma = \sqrt {\sum \limits_{i \in [0, 255]} (x_i - 127)^2 \cdot {count(x_i) \over {H \cdot W}}}[/math]

Is this correct? All I can find is shit about the properties of the standard deviation and no algorithm to calculate it.

>>8211352
>Assuming all values are equally probable
If that were the case, you wouldn't need to calculate [math] p_i [/math] in the next line. So [math] \mu [/math] should actually be [math] \sum \limits_{i} p_i x_i [/math].
The formula for [math] p_i [/math] is correct but I think it's more appropriate to call it relative frequency rather than probability.

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How do I count the probability that xDy rolls higher than xDy+z?
For example: 2D10 vs. 2D10+5

>>8211476
To clarify: The probability of 2 10-sided die added together rolling higher than another pair of 10-sided die added together with an additional 5 added to their result.

>>8211430
So I end up with this, right?

[math]\sigma = \sqrt{\sum \limits_{i \in [0 .. 255]} ({x_i - \sum \limits_{j \in [0 ..255]} (p_j} \cdot x_j))^2 \cdot p_i}[/math]

where

[math]p_i = {count(x_i) \over {H \cdot W}}[/math]

I calculated an example, does this seem right?

[math]
W := 8 \\
H := 8 \\
x_{255} := 255 \\
x_n := 0; n \neq 255 \\
I = \left( \matrix{0 & 0 & 255 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0} \right) \\
H \cdot W = 64 \\
count(0) = 63 \\
count(255) = 1 \\
count(x) = 0; x \neq 0; x \neq 255 \\
p_0 = {count(0) \over {H \cdot W}} = {63 \over 64} \\
p_{255} = {1 \over 64} \\
p_x = 0 \\
\mu= p_0 \cdot x_0 + p_{255} \cdot x_{255} \\
\mu= {255 \over 64} \\
\sigma^2 = (x_0 - \mu)^2 \cdot p_0 + (x_{255} - \mu)^2 \cdot p_{255} \\
\sigma^2 \approx 1000 \\
\sigma = \sqrt{\sigma^2} \\
\sigma \approx 32
[/math]

>>8211512
Seems correct, but x_n is n for all n.

>>8211528
Whoops, you're right. Thank you.
Will hack that into my program and see what comes out.

How do we detect and measure antimatter if it would theoretically destroy any instruments that came in contact with it?

>>8211604
Charge? Inducted magnetic field?
Antimatter has opposite charge as its pair.

I flushed my house keys down the toilet I think. What's chance of getting them back after septic tank truck drains faeces from my cesspool?

i've been trying to wrap my head around the maxwell-boltzmann distribution
i understand that it assumes velocities are normally distributed along the x, y and z axes and goes from there
problem is, every resource i've found on normal distribution only has the equation and not how the equation is derived, and i don't know where to start myself. should i divide it into n binary distributions (+1/n or -1/n with equal weight) and see what i get when n->infinity?

>>8211476
> How do I count the probability that xDy rolls higher than xDy+z?
It's the sum of P(i)*P(j) for all i, for all i>j+z, where P(n) is the probability of rolling n.

The probability of getting i from one roll and j from another is P(i)*P(j), so you sum this for all i,j which satisfy the criteria (i.e. one roll exceeds the other by more than z).

Note that there isn't a closed-form solution. There isn't even a simple closed form for the probability of rolling n from xDy unless y=2 (i.e. the binomial distribution).

>>8211814
thank you

how would a game like roy from rick and morty work?
would you perceive time as though you were in a reverse speedforce?
or would you perceive 50+ years going by at regular speed despite only playing for a half hour or so?

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What textbook or internet courses did some of you take to understand Electronics?

Most of the books I've found through google have been too complicated for me. Others meddle quite early with calculus / differential equations and I've little to no knowledge of both.

My goal is to understand how to build electronic devices but I just don't know what to use as a guide since I am retarded.

please help?

>>8212344
who is this cosplayer

>>8212345

my waifu.

>>8212349
qt

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>>8212351

Its Anzuu

Apparently shes anorexic.

>>8212355
dayum dat cute face :o

>>8212344
Learn some calc dude.
Its the language to describe change and circuits that don't change are boring.

That being said we used Hands On Elctronics by Kaplan.
There's probably a baby bit of electronics in the RC section, but I think the transistor section is devoid of calc and the op amp section you can skip over the circuits that don't make sense.

>>8212358
* baby bit of calc.

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>>8212357
Too cute for this world.

>>8212344
>Others meddle quite early with calculus / differential equations and I've little to no knowledge of both.

then learn. the shit you are describing is why i make $100 an hour proofing peoples retarded electrical designs because they don't have the stones to learn some simple math.

and yes, calculus/ODE's is simple as fuck. the people that struggle with it are the ones who don't have a grasp on algebra and trig to begin with.

>>8212363

Whoa dude chill, I am trying. I did download like some Analysis math books but I've never ever been introduced to this type of rigorous complex math.

I think it was a month ago when I learn of what a ''proof'' is, however I dont know how to do one.

All the calculus I know is how to use certain formulas to either derivate and integrate, which is what they taught us at college.

>>8212365
>this type of rigorous complex math
i'm an engineer. nothing about what i studied is rigorous or complex.

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>>8212366

Well it is to me :P

how many cells inside an ovum?

>>8212377

About three fiddy

Hi /sci/.

I'm giving a presentation in a microbiology class I'm taking. It needs to be about a disease that afflicts humans, but is not very well known. I'm looking for such a disease that also has unique characteristics to it. Any suggestions are much appreciated.

Looking for help with an equation for a program I'm trying to write.

Lets say we have two variables:

One is Y and one is X.
I need to know what to multiply X by so it is always 10% of Y.

>>8213191
if you already know y, just assign
x <- 0.1 * y

>>8213229
I ended up trying Mult = (y*.10)/X

The point is I need an image to be the size of a fraction of another image but I'm just not getting the results I need.

If you're interested here's the code
https://github.com/Enoz/InfiniPad/blob/master/InfiniPad/PaintHelp.cs#L163

>>8199564
Take its companion matrix and use QR algorithm or something similar to approximate it's eigenvalues
>>8199570
Newton method is suboptimal since you only get one root of the polynomial

>>8213263
Additionally Newton's method won't find any complex roots

>>8209436
Nah. Most people would just just use analytical continuation from the rationals as definition which preserves its properties

if i already have this water filter:

https://www.amazon.com/APEC-Premium-5-Stage-Reverse-Drinking/dp/B00I0ZGOZM/ref=sr_1_2?ie=UTF8&qid=1468736268&sr=8-2&keywords=kitchen+water+filter&refinements=p_72%3A2661618011

would attaching this one do anything at all?

https://www.pur.com/water-filtration/water-faucet-mounts/pur-basic-faucet-water-filter

>>8213319
Yeah, just remember you may end up filtering out minerals

>>8213353
4% of chlorine escapes the first filter and there remains a 25 TDS (Total Dissolved Solid) from the first filter. I want to filter out all minerals, i only want H20. I'll get minerals from my food

>>8207500
explain please

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Why do we have the limits in the form 1/2 * | a1 - a2 | ?

I also checked proof wiki and, in order to prove this theorem, they follow the same procedure in which Epsilon equals | L - M | / 2

Why?

>>8213827
I believe they just want something less than the magnitude of the difference. You could divide by 3 or 4 instead and get the same result.

>>8213827
Because when you go through the proof you use the triangle inequality to split up an absolute value into two, each comparable with |a_1-a_2|, and so this appropriately chosen epsilon gives you a contradiction

>>8213591
The distribution is clearly not bell shapes, the tails flatten in an almost linear fashion

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One can easily compute homology groups for the "triangular parachute" X, i.e. the space obtained by taking a 2-simplex and gluing all three vertices together. This gives a copy of S^2 with three holes joined at a point, and these holes have boundaries a,b,c. The surprising thing, to me, is that [math]H_1(X) \cong \mathbb Z \oplus \mathbb Z[/math]. What happens is that one of the boundaries is simply the sum of the other two. I'm not seeing why this should be the case geometrically. Any ideas?

Why do humans exhibit so much more genetic variation in their offspring than other animals?

>>8214006
We live -everywhere-, and have for a very long time, and natural nomadic tendencies have ensured extreme genetic diversity.

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Can someone spotcheck this proof?

>>8214080
Question is: A useless state in a Turing machine is one that is never entered on any input string. Consider the problem of testing whether a Turing machine has any useless states. Formulate this problem as a language and show that it is undecidable.

>>8213992
It's been a while since I've done this stuff but it's not just because going around the last boundary is basically the same as going around the other two boundaries because it's the "compliment" in some sense. You can just move the curve over the sphere and wrap it around the other two boundaries? It's been to long to attempt this rigorously.

>>8214103
Oh, yes! I totally see it now. A loop wrapping around two boundaries is exactly a loop wrapping around the boundary that is left out, since it splits the space into two pieces.

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if a frog has 13 pair of chromosomes

how many cells does the ovum have?

>>8214440
bump

>>8212369
qt

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I have no idea how to solve these types of questions, I'm not even entirely sure what solving means here.

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>>8214643
U is the total energy.

U/V is the density, where V is volume

Plug in L and I into U, then divide by the volume.

>>8214667
Ah, that works nicely!

>>8212403
The Andromeda Strain.

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Will this plane take off?

>>8215166
No, E = mc2 newfag

>>8215166
Planes already have a difficult time taking off on a surface that doesn't move let alone a surface constantly moving.

So no it will never take off, it might however move off the surface. But never take off upwards.

>>8215166
Yes. It is building up greater air pressure under the wings
>Take off without moving
>Good luck building a treadmill strong enough tho

>>8215166
The lift of the plane is the result of air moving above and below its wings. So no, there will be no lift.

>>8213866
And if the right tail was cut off?

>>8215476
You're assuming that the treadmill prevents the plane from moving forward.

A plane's forward motion comes from the propeller, not the wheels. The treadmill would only oppose the plane's motion via friction at the axles.

With "perfect" wheels (frictionless axle), the treadmill would have no effect (unless it's moving so fast the the wheels disintegrate due to centrifugal force).

Even with realistic wheels, the treadmill would need to be moving quite fast to hinder the plane's motion. Friction force is roughly constant; it isn't directly proportional to speed (although increased speed increases power which increases heating which may indirectly increase friction).

>>8215647
I was assumed the 2 arrows implied that the plane does not move.

Of course, if it were able to move fast enough it would take off.

>>8216080
> I was assumed the 2 arrows implied that the plane does not move.
Not sure why you'd assume that.

I'd assume that the red arrow implies that the treadmill is moving backward and the yellow arrow implies that the propeller is pushing the plane forward (this isn't a given; turboprop aircraft can typically reverse the thrust).

It's likely to be rather hard to inhibit a plane's motion with a treadmill.

But then I guess that's the whole point of this troll question: to have people assume things then make an argument based upon unstated assumptions.

I'm reading about relativity and mass and time and all that.
One of the things I read said that increasing the kinetic energy of an object increases its mass.
But I thought that kinetic energy was a relative property, in that an object's kinetic energy can only be measured from the frame of reference of another object.
Mass, on the other hand, does not change based on frame of reference.

How can an increase in a relative property of an object prompt an increase in an objective property of the object, its mass?

>>8216937
> an objective property of the object, its mass?
Mass isn't an objective property; it's relative to the observer.

>>8217309
I get it, relativistic mass and invariant mass are different things. The relativistic mass seems to be what changes.

Is an object's gravity based on its invariant mass, or its current relativistic mass?
Does gravity change with frame of reference?