I typically deal with piecewise linear functions defined over a triangle mesh (values defined per vertex). I can plot this over a 2d triangle mesh domain using the trisurf function:
trisurf(F,V(:,1),V(:,2),S);
I wrap this into my own function tsurf to make it easier to call since I call them so often:
tsurf(F,[V S]);
Sometimes I deal with piecewise constant functions (values defined per triangle). To plot this I use:
tsurf(bsxfun(@plus,size(F,1)*(0:size(F,2)-1),(1:size(F,1))'),[V(F(:),:) repmat(S,size(F,2),1)]);
Or broken down:
% positions of all "Corners"
C = V(F(:),:);
% Scalar field defined at corners
SC = repmat(S,size(F,2),1);
% new disjoint triangle indices into C for each original triangle
FC = bsxfun(@plus,size(F,1)*(0:size(F,2)-1),(1:size(F,1))');
% plot each triangle as piecewise linear function (each of which happens to be constant)
tsurf(FC,[C SC]);
