# Recent content by colstat

1. ### How to make matrix positive definite (when it is not)?

I was hoping to "make" it positive using some trick, but after looking around again I am wrong. Like you said, if it's NOT positive definite, then it's not. I also realized there's an error when putting together the matrix. So, problem solved I guess.
2. ### How to make matrix positive definite (when it is not)?

Suppose I have a matrix that looks like this [,1] [,2] [1,] 2.415212e-09 9.748863e-10 [2,] -2.415212e-09 5.029136e-10 How do I make it positive definite? I am not looking for specific numerical value answer, but a general approach to this problem. I have heard...
3. ### What is copulas exactly, in probability and finance terms

I am not using R, but even in R there's an algorithm right? Is there a way to see what they did in the package?
4. ### What is copulas exactly, in probability and finance terms

Thank you zlin034. What do you use to simulate copulas, Gaussian and student-t? I have two ideas for bivariate Gaussian: 1. integrate the density from Wiki, here http://en.wikipedia.org/wiki/Copula_(probability_theory)#Gaussian_copula or this...
5. ### What is copulas exactly, in probability and finance terms

Hi, all I have been reading about copula, but still very confused. What exactly is a copula? My understanding is: there are couple of components 1. uniform cdf marginal 2. a covariance matrix What exactly is this thing? Why am I calculating the marginals and what does it have to do...
6. ### How to integrate x^(-a)*e^(-b/x), where a, b are constants?

wow, you are really good. Yes, I wrote a simplified version of inverse-gamma. I am looking for the posterior distribution.
7. ### How to integrate x^(-a)*e^(-b/x), where a, b are constants?

Homework Statement How do you integrate this? x-ae-b/x, where a and b are some constants. The Attempt at a Solution I have tried this http://integrals.wolfram.com/index.jsp?expr=x+*+e^%28-1%2Fx%29&random=false Is there a closed form of this?
8. ### What kind of test should I use for before and after treatment

I was wondering about this, since the researcher himself said "binomial distribution z statistics with continuity correction." Also, he said "The P values were calculated by comparing the observed proportion based on 29 patients..." I am just thinking...what in the world?! why? The article...
9. ### What kind of test should I use for before and after treatment

thanks! :) So, why am I told to use normal approximation to the binomial. I understand the normal part, but not the binomial part, where that does binomial come from? Here is another site that actually explains it, but I am still confused...
10. ### What kind of test should I use for before and after treatment

What test or distribution should I use for before and after treatment? Say, I have 30 subjects I test their blood before and after a pill they take a pill, what kind of test should I use? I want to test mean difference, so, paired t-test? or Wilcoxon signed rank test? The data looks like this...
11. ### Proof for upper bounded sets

Why is limit point called a limit point? does it have to do with limits? I know if you talk intervals on a real line in 1-d, you can talk convergence. But when we talk about 2-d, like open balls, why are we calling it limit point, even the definition of a limit point does not mention anything...
12. ### Proof for upper bounded sets

hey, Fredrik. I figured it out. Yes, this is the ultrametric space. Thanks, just wanted to know I am thinking right. For the standard metric. If I have a closed ball, is the interior point same the limit point? I mean the definition of interior point is, open ball B(x,r) is contained in...
13. ### Proof for upper bounded sets

thanks a lot, Deveno. To prove an open ball B(x,r) is also closed. Is it ok to start like this? Let p be a limit point of B(x,r). If p\notinB(x,r), then, p\inB^{c}(x,r). Where I said "let p be a limit point of B(x,r)." I though limit point only existed in closed balls, but B(x,r)...
14. ### Proof for upper bounded sets

wow, that was such a long post. When you say an open set is a union of open balls. How do you actually write that in proof? For all x \in X, there is a ε>0, such that B(x,r) is completely contained in E. Does this look good?
15. ### Proof for upper bounded sets

yessss, that makes sense to me. What exactly is an open set, what is its role in all this? I have read it in Rudin and Wiki. It's saying... say, we are in some space E, we have a point y≠x such that d(x,y)<ε. Another way is to say that every open ball B(x,ε) is completely contained in E...