function v = decoupaux(a,b,x)
A1  = - x(c2i([0 0])) + x(c2i([1 0])) + 3*x(c2i([0 1])) + x(c2i([1 1]));
B1  =   x(c2i([0 0])) - x(c2i([1 0])) - 3*x(c2i([0 1])) - x(c2i([1 1]));
A2 =   x(c2i([0 0])) + x(c2i([1 0])) -   x(c2i([0 1])) - x(c2i([1 1]));
B2 = - x(c2i([0 0])) - x(c2i([1 0])) +   x(c2i([0 1])) + x(c2i([1 1]));
v = a*A1 + b*B1 + a^2*A2 + b^2*B2;

return

function i=c2i(c)
global m n
dims = repmat(m,[1 n]);
i = coord2ind(c+1,dims);
return