Thread Subject:

Problem with the time-efficiency of the code

Hello,

I would like to improve the time efficiency of my code (see below):

//========================================
//There is a structure "s" consisted of delaunay triangulations of different geometrical objects.
s = struct('tess', {});
<<...>>
//E.g.
s(1).tess = DelaunayTri(v(:,1),v(:,2),v(:,3));

// This function veryfies the intersection of all faces of tetrahedrons with the curve
function answer = f1(...);
tessqty = length(s(:));
P1 = []; P2 = []; P3 = [];
for i = 1 : tessqty
   tess = s(i).tess;
   faces = [tess(:,[1 2 3]); tess(:,[2 3 4]); ...
            tess(:,[1 3 4]); tess(:,[1 2 4])];
   P1 = [P1; s(i).tess.X(faces(:,1),1) s(i).tess.X(faces(:,1),2) s(i).tess.X(faces(:,1),3)];
   P2 = [P2; s(i).tess.X(faces(:,2),1) s(i).tess.X(faces(:,2),2) s(i).tess.X(faces(:,2),3)];
   P3 = [P3; s(i).tess.X(faces(:,3),1) s(i).tess.X(faces(:,3),2) s(i).tess.X(faces(:,3),3)];
end
walk = ones(leng,1);
for j = 1 : leng
    for i = 1 : length(P1(:,1))
        [flag,u,v,a] = rayTriangleIntersection(origin(j,:),direct(j,:),P1(i,:),P2(i,:),P3(i,:));
            if flag == 1
                intersection = origin(j,:) + a*direct(j,:);
                if pointSegment(intersection,origin(j,:),dest(j,:))
                    walk(j) = 0;
                    break,
                end
            end;
    end;
end;
answer = walk;
end;
//========================================

This function "f1" is executed inside the FOR LOOP (with 100 iterations). Totally, it takes a very long time (>30 minutes) to run the code. I was thinking about the vectorization of the code, but it doesn't work for the structure "s".

I would appreciate any help. Perhaps, someone could share the experience. Thanks a lot.

"Liana" wrote in message <j4dvlg$beb$1@newscl01ah.mathworks.com>...
>
> P1 = []; P2 = []; P3 = [];
> for i = 1 : tessqty
> tess = s(i).tess;
> faces = [tess(:,[1 2 3]); tess(:,[2 3 4]); ...
> tess(:,[1 3 4]); tess(:,[1 2 4])];
> P1 = [P1; s(i).tess.X(faces(:,1),1) s(i).tess.X(faces(:,1),2) s(i).tess.X(faces(:,1),3)];
==================

Tsk,Tsk. Growing the arrays P1,P2,P3 inside a for-loop? You should know better....






> This function "f1" is executed inside the FOR LOOP (with 100 iterations). Totally, it takes a very long time (>30 minutes) to run the code. I was thinking about the vectorization of the code, but it doesn't work for the structure "s".
=====================

So, about 20 sec per iteration of f1?

Anyway, apart from my point above, we have no way of knowing how many iterations your for-loop runs for, or how much overhead is contributed by some of the functions you're calling like rayTriangleIntersection. See "doc profile" for ways of analyzing this.

"Matt J" wrote in message <j4f6i1$i9g$1@newscl01ah.mathworks.com>...
>
>
> Tsk,Tsk. Growing the arrays P1,P2,P3 inside a for-loop? You should know better....
==================

In particular, recall this thread, where we talked about not doing this

http://www.mathworks.com/matlabcentral/newsreader/view_thread/306613#832590