Recent content by xnull

  1. X

    Can every ideal be decomposed into a triangular Groebner basis?

    Groebner basis calculations are an important technique for solving systems of nonlinear equations. Despite being (in the worst case), computationally intractable, they seem to be effective solutions for a multitude of problems. I have a problem that I am trying to solve. I have perused the...
  2. X

    How many even subsets are there?

    Solved it. Heh. Silly to have missed it. 2^{m-1} even subsets and odd subsets.
  3. X

    How many even subsets are there?

    Given a finite set S of cardinality m: Decide how many even or odd subsets there are of S (finding one should give you the other). Here is what I've done so far. First, I looked to a multiplication out by hand. (m * (m-1)) + (m * (m-1) * (m-2) * (m-3)) + (m * (m-1) * (m-2) * (m-3) * (m-4) *...
  4. X

    Generating a Permutation Matrix P for All Permutations of A

    Oh phoey! Thank you Moo of Doom (and the greater whole that is PF).
  5. X

    Generating a Permutation Matrix P for All Permutations of A

    Let me ask it another way... Is there some permutation that can be done to a list of elements such that the recursive application of that permutation to that list will cycle through all possible permutations? Basically I'd like something like C++'s next_permutation (but without having each...
  6. X

    Generating a Permutation Matrix P for All Permutations of A

    Hello! I was wondering if there is a way to generate a permutation matrix P such that each application of P to another matrix A will find the "next" permutation of A. I'm looking for a way to generate a permutation matrix P (size m x m) such that applying it m! times to A (m x m) returns A...
  7. X

    Does a number n exist where 2^n mod 3 = 0?

    Ahh, that's very clear.
  8. X

    Does a number n exist where 2^n mod 3 = 0?

    matt grime, I am eager to understand why my attempt at a formal proof is invalid. I'm not certain from your post what I have done wrong. Could you explain it again?
  9. X

    Does a number n exist where 2^n mod 3 = 0?

    My attempt at a formal proof by induction. For a number x in the set of natural numbers, prove that there is no value for x such that 2^x mod 3 = 0. For some number n mod 3 to be equal to 0, 3 must be a number in n's prime factorization. Assume that 2^x mod 3 != 0. 2^x has a prime...
  10. X

    Layperson's description of multivariate gaussian distributions?

    Wow, D H, you went all out. Thank you many times. I really understand this now! My experiences with this forum (the few) have been exceptional. I posted the same question on two different forums - one focused on math and the other with a focus on statistics. Only this forum responded. And the...
  11. X

    Layperson's description of multivariate gaussian distributions?

    Yes, precisely. I'm using this for unsupervised learning. Phrak, if you want to get help on the EM algorithm you should start another thread so that it is more easily searchable by Googlers. I'll be sure to keep my eye out in case you do. Thank you D F. That was precisely the type of...
  12. X

    Layperson's description of multivariate gaussian distributions?

    http://en.wikipedia.org/wiki/Multivariate_normal_distribution
  13. X

    Prove that the law of excluded middle does not hold in some many-valued logic

    "can we show that for some condition, there is P with ¬(P∨¬P) ?" There exists a P such that ¬(P∨¬P) There exists a P such that ¬P Λ P Lets prove this by contradiction. It seems really easy, although I'm not sure if it is valid since the law of excluded middle isn't meant to be applied to...
  14. X

    Layperson's description of multivariate gaussian distributions?

    Thank you mathman! I am looking for an undergraduate level explanation of how the multivariate guassian distribution's pdf got deduced. All the while I'm looking for the rationale behind the math - little sentences which explain why each step is justified if it isn't obvious and little...
  15. X

    Smoothing algorithm for times series and slope measurement

    Foremost: I am an undergraduate CS student and therefore my advise should be taken with a skeptical ear. I think it depends on what you want to use the smoothed values for. If you want to do some sort of predictions or make a general model of the data I think what you want to do is model the...
Back
Top