## Search found 527 matches

Mon Jan 05, 2015 1:34 am UTC
Forum: Mathematics
Topic: Probability of drawing a number from a normal distribution.
Replies: 2
Views: 1217

### Re: Probability of drawing a number from a normal distributi

Ah, you're right. I overcomplicated things by expanding the expression. That makes sense, thanks
Mon Jan 05, 2015 12:35 am UTC
Forum: Mathematics
Topic: Probability of drawing a number from a normal distribution.
Replies: 2
Views: 1217

### Probability of drawing a number from a normal distribution.

(not hw) Suppose someone sampled a number Q from the standard normal distribution. Provided that Q is in the set {x_1, x_2, .... x_n}, how can I compute the probabilities that Q = x_1 or Q = x_2... --- If I let K(x, ɛ) be the probability that a sample from the normal distribution is in the range (x,...
Thu Jan 01, 2015 8:04 pm UTC
Forum: Mathematics
Topic: how to resample from weighed points (statistics)
Replies: 3
Views: 1399

### Re: how to resample from weighed points (statistics)

I see, thanks for the notes. So basically, we can just individually pull samples from our previous set until we have our quota.
Thu Jan 01, 2015 3:51 pm UTC
Forum: Mathematics
Topic: how to resample from weighed points (statistics)
Replies: 3
Views: 1399

### how to resample from weighed points (statistics)

(not hw) I'm trying to figure out the particle filter. Specifically, how the resampling part is done. Given a set of weighed points, i need to create a new distribution of unweighted points where more points are present in areas of higher weights. For a more easy to visualize explanation of the prob...
Fri Nov 28, 2014 1:47 am UTC
Forum: Mathematics
Topic: Clarification on definition of category
Replies: 6
Views: 2631

### Re: Clarification on definition of category

I see, that makes sense. thanks!
Thu Nov 27, 2014 4:52 pm UTC
Forum: Mathematics
Topic: Clarification on definition of category
Replies: 6
Views: 2631

### Re: Clarification on definition of category

Moole's example shows the important of the composition association property, but the identity part still confuses me LetterX, you said that "But now you can check that there's no identity element, because we excluded the map f_0, so anytime we compose f_n with any other f_m, we'll get an f_{n+m...
Thu Nov 27, 2014 3:06 pm UTC
Forum: Mathematics
Topic: Clarification on definition of category
Replies: 6
Views: 2631

### Clarification on definition of category

A book i'm reading claims that this makes a category: https://i.imgur.com/P0pY2dH.png What confuses me is the identity and associative properties -- It seems like they would be true for all object A, B, C, D... etc I went on wikipedia https://en.wikipedia.org/wiki/Category_%28mathematics%29#Definiti...
Thu Nov 27, 2014 2:52 pm UTC
Forum: Coding
Topic: Understanding call/cc
Replies: 6
Views: 3870

### Re: Understanding call/cc

I can't wait to use start subtle coughing with this :)
Thu Nov 27, 2014 8:00 am UTC
Forum: Coding
Topic: Understanding call/cc
Replies: 6
Views: 3870

### Re: Understanding call/cc

Oh i see it now, thanks for clearing up my confusion!
Thu Nov 27, 2014 7:24 am UTC
Forum: Coding
Topic: Understanding call/cc
Replies: 6
Views: 3870

### Re: Understanding call/cc

I'm not exactly sure what you mean by "continuation function", a google search just showed a bunch of pages related to call/cc.
Thu Nov 27, 2014 6:46 am UTC
Forum: Coding
Topic: Understanding call/cc
Replies: 6
Views: 3870

### Understanding call/cc

I am trying to understand call/cc. According to this page, http://c2.com/cgi/wiki?CallWithCurrentContinuation "If you're a C programmer, you might find this explanation easier: in C, you can take a pointer to a function. In C, you also have a return statement. Suppose the return statement were ...
Sun Nov 09, 2014 2:25 pm UTC
Forum: Science
Topic: Can protons be extracted from an acid solution?
Replies: 26
Views: 5573

### Re: Can protons be extracted from an acid solution?

my plans are foiled. but good answers, thank you.
Sun Nov 09, 2014 2:30 am UTC
Forum: Science
Topic: Can protons be extracted from an acid solution?
Replies: 26
Views: 5573

### Can protons be extracted from an acid solution?

I've always wanted a beaker of protons.

Suppose a strongly positively charged object is used to remove the Cl- from an HCl solution. The water is then boiled off, leaving only H+ ions.

Does this procedure work? Or why not?
Mon Nov 03, 2014 7:46 pm UTC
Forum: Mathematics
Topic: Limit problem
Replies: 7
Views: 2576

### Re: Limit problem

oh right, L'Hôpital somehow completely slipped from my mind
Mon Nov 03, 2014 3:44 am UTC
Forum: Mathematics
Topic: Limit problem
Replies: 7
Views: 2576

### Re: Limit problem

yes, that was poor variable naming on my part --- it seems to me that this limit seems only solvable because of a coincidental derivative hidden in it. what if cos(b+a) in the expression were replaced with cos(ab)? more generally, are there limits that can't be solved in a closed form just as e^x/x ...
Sun Nov 02, 2014 10:54 pm UTC
Forum: Mathematics
Topic: Limit problem
Replies: 7
Views: 2576

### Re: Limit problem

oh i see it now.

thank you
Sun Nov 02, 2014 10:11 pm UTC
Forum: Mathematics
Topic: Limit problem
Replies: 7
Views: 2576

### Limit problem

(not hw) I'm trying to solve http://latex.codecogs.com/gif.latex?%5Clim_%7Ba%20%5Cto%200%7D%20%5Cfrac%7Bacos%28b%29%7D%7Bcos%28b%29-cos%28a&plus;b%29%7D wolfram alpha tells me it's cot(b), but I can't tell why. i've tried splitting the limit up into the product of two limits, rewriting the cosin...
Sat Nov 01, 2014 1:12 pm UTC
Forum: Science
Topic: How do synchrotrons accelerate ions?
Replies: 2
Views: 1801

### Re: How do synchrotrons accelerate ions?

that explains it, thank you
Sat Nov 01, 2014 5:14 am UTC
Forum: Science
Topic: How do synchrotrons accelerate ions?
Replies: 2
Views: 1801

### How do synchrotrons accelerate ions?

Wikipedia says a synchrotron works similar to a cyclotron, except the magnetic field strength of dependent on time, not space (hence the constant orbital radius). But a cyclotron requires both the magnet to keep the ions orbiting and two D shaped electrodes for the actual acceleration. Obviously the...
Thu Oct 02, 2014 6:42 pm UTC
Forum: Mathematics
Topic: fooling around with points on a plane and optimization
Replies: 7
Views: 3404

### Re: fooling around with points on a plane and optimization

yes.
Thu Oct 02, 2014 10:28 am UTC
Forum: Mathematics
Topic: fooling around with points on a plane and optimization
Replies: 7
Views: 3404

### Re: fooling around with points on a plane and optimization

huh. is this really equivalent to the steiner problem? i don't see it.

@duckshirt the points move because i run scipy.optimize on them. i start in the square, then search for the best arrangement of points, which can be outside the square
Thu Oct 02, 2014 3:14 am UTC
Forum: Mathematics
Topic: fooling around with points on a plane and optimization
Replies: 7
Views: 3404

### fooling around with points on a plane and optimization

It occurred to me that I could arrange 2 or 3 points in a way such as the distance between any two points was exactly one, but that this was impossible for a larger number of points. So I tried anyways. For every pair of points, let the error be the difference between 1 and the distance between the ...
Sun Sep 07, 2014 4:25 pm UTC
Forum: Coding
Topic: Fast pixel drawing (python)
Replies: 7
Views: 13044

### Re: Fast pixel drawing (python)

On the other hand, the PyGame code is very clearly suboptimal. He really should have the random array built, processed in a single pass, and then blit it once per frame. Keep your mind on how memory is traversed, and how caching works to take advantage of CPU prefetchers (ie: traverse all arrays fr...
Sun Sep 07, 2014 5:54 am UTC
Forum: Coding
Topic: Fast pixel drawing (python)
Replies: 7
Views: 13044

### Fast pixel drawing (python)

I want a viewable canvas/image/plot/display where I can quickly manipulate a large amount of pixels individually. However, this is proving to be difficult. Each pixel will be one value in a 1000 by 2000 array, but at most, I will probably only have to manipulate 100,000 (300 x 300) pixels per frame....
Thu Aug 07, 2014 10:59 pm UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### Re: questions from algebra (inverse functions)

Interesting. So if the definition by the book is isomorphism in the context of sets, in what context is kubit's definition? The book i'm reading (Algebra. Chapter 0) later also defines isomorphism for categories and some other things http://tinyurl.com/201352488752 http://tinyurl.com/807142482225
Thu Aug 07, 2014 6:20 pm UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### Re: questions from algebra (inverse functions)

Thank you for the clarification.

this book doesn't mention anything about the relations. Am I missing something or did they just get it wrong?
Thu Aug 07, 2014 5:52 am UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### Re: questions from algebra (inverse functions)

the question hinted something about axiom of choice -- so that makes sense now. i'll keep in mind the tip about using finite examples. by the way, if f bijects A, B means A and B are isomorphic, doesn't |A| = |B| imply A and B are isomorphic and vice versa? since for all bijections, the size of both...
Sun Aug 03, 2014 8:25 pm UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### Re: questions from algebra (inverse functions)

g needs to map B to A. so sqrt(x) would be a right inverse of x^2. i think. and to prove g exists: the graph of f is a collection of ordered pairs where the set of the second element in each of the pairs is B, and the set of the first element in each of the pairs is A. we know this is true because f...
Sun Aug 03, 2014 7:29 pm UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### Re: questions from algebra (inverse functions)

according to the book, a function satisfies (∀a ∈ A) (∃!b ∈ B) f(a) = b proving g exists implies f is surjective if g exists, for every b' in B, there exists one a' s.t. g(b') = a' . this makes f surjective. proving f is surjective implies g exists is this even possible? let U be the set of non-nega...
Sun Aug 03, 2014 6:10 pm UTC
Forum: Mathematics
Topic: questions from algebra (inverse functions)
Replies: 25
Views: 4868

### questions from algebra (inverse functions)

I'm try to prove that the function f has a right inverse iff it is surjective. f: A -> B g is the inverse of f By right inverse i mean f.g = id_B I don't know how to approach the problem. this is one my failed attempts: if for every b' in B, f(g(b')) = b', then f.g = id_B. we know a = g(b) if b = f(...
Sat Aug 02, 2014 11:53 pm UTC
Forum: Mathematics
Topic: the proof is trivial!
Replies: 5
Views: 4914

### the proof is trivial!

because of the three word search limitation, i'm not sure if this has been posted before. nevertheless, it's pretty amusing. hope this is the right forum.

http://www.theproofistrivial.com/
Thu Jul 24, 2014 2:27 am UTC
Forum: Mathematics
Topic: (what is) a multiplicative order of a finite field?
Replies: 8
Views: 3485

### Re: (what is) a multiplicative order of a finite field?

That means N is the least positive integer such that ζ N =1. So is ζ the value in GI for which N is smallest in ζ^N=1? For example, if QI = {1, i, -1}, then ζ = 1 because 1^1 = 1, i^4 = 1, (-1)^2 = 1 does that sound right? ---- Now, look at (x+1)^2 = x^2 + 2x + 1 = 2x = -x (x+1)^3 = -x(x+1) = -x^2 ...
Wed Jul 23, 2014 10:57 pm UTC
Forum: Mathematics
Topic: (what is) a multiplicative order of a finite field?
Replies: 8
Views: 3485

### (what is) a multiplicative order of a finite field?

https://en.wikipedia.org/wiki/Trigonometry_in_Galois_fields#Trigonometry_over_a_Galois_field According to this page, zeta is an element in the multiplicative order GI(q), the gaussian integers over a given galois field. However, the multiplicative order page https://en.wikipedia.org/wiki/Multiplicat...
Sat Jul 19, 2014 3:11 am UTC
Forum: Coding
Topic: function application in lisp, confusing error messages
Replies: 6
Views: 4441

### Re: function application in lisp, confusing error messages

oh, i see what i did wrong now.

thank you for the help, and i'll keep your advice in mind!

btw, would you be able to link me to a ml type notation guide? i did a few standard google searches but couldn't find anything substantial. particularly, what does that * operator do?
Fri Jul 18, 2014 10:47 pm UTC
Forum: Coding
Topic: function application in lisp, confusing error messages
Replies: 6
Views: 4441

### Re: function application in lisp, confusing error messages

thanks for the help. somehow, funcall feels kind of crude and inelegant. ---- this is a bit off topic but i figured it was better than starting a new thread. i've been trying church numerals and arithmetic. it worked up until i tried exponentials. i understand the concept behind the exponentiation f...
Fri Jul 18, 2014 2:24 pm UTC
Forum: Coding
Topic: function application in lisp, confusing error messages
Replies: 6
Views: 4441

### function application in lisp, confusing error messages

(defun repeat (f x n) (if (> n 0) (x) (repeat f (f x) (- n 1)))) (defun foo (z) (+ z 1)) i'm trying to repeatedly apply a function. >(repeat 'foo 4 0) *** - EVAL: undefined function F but foo is defined: > #' foo #<FUNCTION FOO (Z) (DECLARE (SYSTEM::IN-DEFUN FOO)) (BLOCK FOO (+ Z 1))> so removed th...
Sun Jun 29, 2014 4:55 am UTC
Forum: Computer Science
Topic: alpha-beta pruning seems counterintuitive
Replies: 3
Views: 3928

### Re: alpha-beta pruning seems counterintuitive

That analogy makes it easy to understand, thank you!
Thu Jun 26, 2014 9:37 pm UTC
Forum: Computer Science
Topic: alpha-beta pruning seems counterintuitive
Replies: 3
Views: 3928

### alpha-beta pruning seems counterintuitive

according to this pseudocode: https://en.wikipedia.org/wiki/Alpha%E2%80%93beta_pruning#Pseudocode it seems that you stop searching once your expected score is higher than theirs or their expected score is higher (thus beta is lower) than yours. but why would you do that? instead of having a score ma...
Fri Jun 13, 2014 2:56 pm UTC
Forum: Coding
Topic: repetitive code when i try functional programming
Replies: 7
Views: 7060

### Re: repetitive code when i try functional programming

Oh, I didn't know about where. that does make a lot of sense. thank you!
Fri Jun 13, 2014 2:23 pm UTC
Forum: Coding
Topic: repetitive code when i try functional programming
Replies: 7
Views: 7060

### repetitive code when i try functional programming

i'm learning haskell, but i find that in some cases, my code devolves into a lot of repetition. usually i'd write something like def foo(a, b, c, y) x = a**b mod c if x == y or (x*y mod 2) == 0 or x == 1 goo(x+1, x-1) else goo(x+2, x-2) but in haskell, i can't declare x as a variable (or at least i ...