Rectifying compute_curvature.m error in Toolbox Graph in Matlab

I am currently using the Toolbox Graph on the Matlab File Exchange to calculate curvature on 3D surfaces and find them very helpful (<http://www.mathworks.com/matlabcentral/fileexchange/5355>). However, the following error message is issued in “compute_curvature” for certain surface descriptions and the code fails to run completely:

Error in ==> compute_curvature_mod at 75 dp = sum( normal(:,E(:,1)) .* normal(:,E(:,2)), 1 ); ??? Index exceeds matrix dimensions.

This happens only sporadically, but there is no obvious reason why the toolbox works perfectly fine for some surfaces and not for others (of a similar topology). I also noticed that someone had asked about this bug back in March 2009 on File Exchange, but that the question had gone unanswered. The post states

"compute_curvature will generate an error on line 75 ("dp = sum( normal(:,E(:,1)) .* normal(:,E(:,2)), 1 );") for SOME surfaces. The error stems from E containing indices that are out of range which is caused by line 48 ("A = sparse(double(i),double(j),s,n,n);") where A's values eventually entirely make up the E matrix. The problem occurs when the i and j vectors create the same ordered pair twice in which case the sparse function adds the two s vector elements together for that matrix location resulting in a value that is too large to be used as an index on line 75. For example, if i = [1 1] and j = [2 2] and s = [3 4] then A(1,2) will equal 3 + 4 = 7.

The i and j vectors are created here: i = [face(1,:) face(2,:) face(3,:)]; j = [face(2,:) face(3,:) face(1,:)];

Just wanted to add that the error I mentioned is caused by the flipping of the sign of the surface normal of just one face by rearranging the order of the vertices in the face matrix"

I have tried debugging the code myself but have not had any luck. I am wondering if anyone here has solved the problem or could give me insight – I need the code to be sufficiently general-purpose in order to calculate curvature for a variety of surfaces, not just for a select few.

Thanks in advanced.

[iyyakutti iyappan]

http://stackoverflow.com/questions/12922419/rectifying-compute-curvature-m-error-in-toolbox-graph-in-matlab