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# Richard Baker

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1. ## Using GJK for collision detection

I successfully implemented GJK. It is fast, but narrow phase is a bottleneck because i do GJK many times in the binary search. I read about the EPA, expanding poly tope algorithm. Question: EPA returns the point on the CSO closest to the origin. Does this point correspond to the edge/edge or vertex/face to collide first?
2. ## Projected Gauss Seivel Algorithm

I successfully implemented GJK. It is fast, but narrow phase is a bottleneck because i do GJK many times in the binary search. I read about the EPA, expanding poly tope algorithm. Question: EPA returns the point on the CSO closest to the origin. Does this point correspond to the edge/edge or vertex/face to collide first?
3. ## Projected Gauss Seivel Algorithm

Thanks for the responses. As it turns out, I was incorrectly binding dynamic friction to equal zero if there was enough force to break static friction but still zero tangential velocity. If instead I just let PGS work its magic, the non-zero friction at each vertex cancels out so that an object at rest will continue at rest. Unfortunately, I don't know much about parallel processing on the GPU. But that will probably be my next step after extending to 3D. I suppose in a multi-player online setting the GPU can perform server-side computations such as if a grenade starts to slide or grow after bouncing a few times? Thanks again.
4. ## Projected Gauss Seivel Algorithm

I am using PGS to solve the contact force part of my rigid body simulator (2D for now). It seems to be functional but I can only seem to get a few decimals worth of accuracy. The algorithm will start cycling between different values. I realize that due to the lack of uniqueness theorem that there are many solutions to the NCP due to the introduction of friction. I want to find one solution that works and I feel that this cycling reduces accuracy. I tried subspace minimization but that doesn't seem to fix the problem. Fingers crossed that someone can help me. Thank You.
5. ## Baraff pivoting lcp

This is about the paper "Fast contact force computation for non-penetrating rigid bodies". Has anybody made sense of this? I have questions. Do I completely neglect the unprocessed a's that are neither mc nor c? If the sign for an unprocessed "a" changes, should I stop and pivot and put that index in either nc or c? I know that the unprocessed "f's" remain zero, but what if the sign of an unprocessed "a" changes? Do I actually perform a pivot operation on a matrix? Or is that done by moving between a "c" and an "mc"?
6. ## probability distribution of a function

I have a function y (x) defined over a range from x0 to x1 I want to know the probability that y will equal some number within a given interval if I choose a random value for x.
7. ## Statistics textbook

Now my son wants a statistics textbook. (for the uninitiated, I am only his humble scribe and mother). I remember my stats textbooks from 35 years ago in grad school (Statistics: An Intuitive Approach: Weinberg, George H.: 9780818504266: Amazon.com: Books), but they are not necessarily the best today. He wants one that will take him from relatively basic stuff up to regression analysis. If not one, then two in a series. Hopefully something that is inexpensive and/or available secondhand through Amazon. Suggestions? Thank you.
8. ## Factoring a sine wave

The normalizing factor m = 1/(pi2*{2pi}2*{3pi}2*...{npi}2) I derived this from the products formula but it is only valid for x in the neighborhood of 0. It was a neat exercise but I don't totally understand why m should equal this but it is cool nonetheless.
9. ## Factoring a sine wave

Thank you. I will be watching the thread for other responses.
10. ## Factoring a sine wave

If you look at the graph of sin (x) you see that all the zeroes are located at multiples of pi. So if you were to factor sin (x) as if it were a polynomial you would get m * x * (x-pi) * (x + pi) * ( x-2pi) * (x + 2pi) * ( x - 3pi ) * (x + 3pi) ..... (x - n pi) * ( x + n pi) as n approaches infinity. Question: what is m? I figured this much from computer experiments, m is not a constant, it is a function of x and n. m is less than 0 if n is odd, m is greater than 0 if n is even. If you graph abs (x) and scaled it by the appropriate very large factor you'd see that m (x) looks like a bump centered at x =0 which morphs as n increases, it retains the bump figure. It is not of the form c * exp ( - k x2), although it looks like it could be. What is this mystery function m? Please help me figure this out.
11. ## Alternatives to z buffering

Thank you again.
12. ## Alternatives to z buffering

I already used back face culling on some polygons but not all of them. I tried using the average z value of the vertices of the polygon but that doesn't work because some polygons have closer points but are further away from the average. Thank you. Be back later in a rush right now.
13. ## Alternatives to z buffering

I am working on a platform that does not have z buffering hardware support. I am trying to sort polygons in a scene according to z distance so I can implement the painter's algorithm, but I am having no luck. Currently I divide the game into regions and sort the polygons manually in each region according to what looks right. But I would like to know the mathematical solution. I don't have any cyclical overlaps and I don't have any intersecting objects but I do have polygons that touch. Thank you for your help.
14. ## My ray-tracing algorithm

He has decided that William of Occam had a better idea.
15. ## My ray-tracing algorithm

Sensei or others-- I have received a copy of the code for his problem. Others, ask and you shall receive.
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