如何向量化numpy中嵌套的for循环

v,u,j=file.shape
for v in range(height):
  for u in range(width):
    start[v,u,0] = -0.5 + u / (width-1)
    start[v,u,1] = (-0.5 + v / (height-1)) * height / width
    start[v,u,2] = 0

   v,u,j=file.shape
   x,y,z=np.mgrid(0:v,0:u,0:j)