compute_edge_face_ring.sci

function A = compute_edge_face_ring(face)

// compute_edge_face_ring - compute faces adjacent to each edge
//
//   e2f = compute_edge_face_ring(face);
//
//   e2f(i,j) and e2f(j,i) are the number of the two faces adjacent to
//   edge (i,j).
//
//   Copyright (c) 2007 Gabriel Peyre


[tmp,face] = check_face_vertex([],face);

n = max(face(:));
m = size(face,2);
i = [face(1,:) face(2,:) face(3,:)];
j = [face(2,:) face(3,:) face(1,:)];
s = [1:m 1:m 1:m];

// first without duplicate
[tmp,I] = unique( i+(max(i)+1)*j );
// remaining items
J = setdiff(1:length(s), I);

// flip the duplicates
i1 = [i(I) j(J)];
j1 = [j(I) i(J)];
s = [s(I) s(J)];

// remove doublons
[tmp,I] = unique( i1+(max(i1)+1)*j1 );
i1 = i1(I); j1 = j1(I); s = s(I);

A = make_sparse(i1,j1,s);


// add missing points
I = find( A'~=0 );
I = I( A(I)==0 ); 

// bug
// A( I ) = -1;
[x,y] = ind2sub([n n],I);
for i=1:length(x)
    A(x(i),y(i)) = -1;
end

endfunction