You say that
t=[]_3*39436
If we are to understand that t is 3 x 39436, then
T=sparse(t([1 4 2 5 3 6],:),t([4 2 5 3 6 1],:),1,np,np);
This attempts to access up to row 6 out of the 3 rows, so that would be a problem.
Glancing at the code, I see that just above that point there is a test as to whether T has exactly 4 rows, with only rows 1, 2, and 3 being used in that case. I see that t appears to correspond to a triangulation . The documentation for pdeplot describes t as,
"Mesh triangles, specified as a 4-by-Nt matrix of triangles, where Nt is the number of triangles in the mesh."
"In the Triangle matrix t, the first three rows contain indices to the corner points, given in counter clockwise order, and the fourth row contains the subdomain number."
Therefore a 3 x something triangulation matrix was invalid in R2009b and is invalid now.
