code: def _affine_mult(c:FlowField,m:AffineMatrix)->FlowField:
      "Multiply `c` by `m` - can adjust for rectangular shaped `c`."
      if m is None: return c
      size = c.flow.size()
      h,w = c.size
      m[0,1] *= h/w
      m[1,0] *= w/h
      c.flow = c.flow.view(-1,2)
      c.flow = torch.addmm(m[:2,2], c.flow,  m[:2,:2].t()).view(size)
      return f _affine_mult(c:FlowField,m:AffineMatrix)->FlowField:
      "Multiply `c` by `m` - can adjust for rectangular shaped `c`."
      if m is None: return c
      size = c.flow.size()
      h,w = c.size
      m[0,1] *= h/w
      m[1,0] *= w/h
      c.flow = c.flow.view(-1,2)
      c.flow = torch.addmm(m[:2,2], c.flow,  m[:2,:2].t()).view(size)
      return c
docs: Multiply `c` by `m` - can adjust for rectangular shaped `c`.