interpolation coefficients in tri2grid

I could not find an explanation as to how to use the interpolation coefficients (a2 and a3) that are returned by tri2grid: [uxy,tn,a2,a3]=tri2grid(p,t,u,x,y). I would like to export these and allow users without Matlab to interpolate the solution to points not on the mesh vertices. I am familiar with there being three coefficients that relate solution at arbitrary point (x,y) to solutions on vertices of triangle in which (x,y) is located. To wit: u(x,y) = a1*u1 + a2*u2 + a3*u3 (for linear interpolation). I can only imagine that the a2 and a3 from tri2grid are normalized in some fashion and equivalent to these (possibly by area of triangle???)

A related question (I think): what can one do with the a1, a2, a3 coefficients returned by pdetrg. That is, the a1,2,3 in [ar,a1,a2,a3]=pdetrg(p,t). I wonder if I can do the interpolations with these. My sense is that they are related to the a2, a3 from tri2grid.

[Richard Garner]

I have (partially) figured out the answer to my question. Depends on whether 2*area of triangle has been divided out. From a finite element textbook that I have, a1+a2+a3=2A, where A=area of triangle. If 2A has been divided out (in Matlab's tri2grid(), then a1+a2+a3=1. I suspect it is the latter from inspection of the tri2grid function (if a2 and a3 are used as inputs, then toward the end it has uxy=(1-a2-a3)*u1+a2*u2+a3*u3. In any case, it would be good if the Mathworks folks be more explicit about this in the documentation.

[elisabetta carlini]

Hello Richard, how you find out how to interpolate a function defined on a triangular mesh to an array of arbitrary points? Thanks Elisabetta

[John D'Errico]

Elisabeth - Note that you have made this into a zombie question, re-animated years after this individual has even bothered to visit this web site. So ask your question on Answers directly, at least if you hope for an answer.