def perspective(t, b, l, r, n, f):
    return array(((2*n/(r-l), 0 , (r+l)*(r-l), 0),
                  (0,2*n/(t-b),(t+b)/(t-b),0)
                  (0,0,-(f+n)/(f-n),-2*f*n/(f-n)),
                  (0,0,-1,0)))