def tensor(a,b): '''Returns the 3x3x3 (27 element) trifocal tensor given two 3x4 camera matrices. ''' T = zeros((3,3,3)) for ti in range(3): i = ti for tj in range(3): for tk in range(3): for j in range(tj+1): for k in range(tk+1): T[ti,tj,tk] += a[j,i]*b[k,3] - a[j,3]*b[k,i] return T