def forward(self, cls_pred, box_pred, cls_target, box_target):
cls_pred, box_pred, cls_target, box_target = [_as_list(x) \
for x in (cls_pred, box_pred, cls_target, box_target)]
# cross device reduction to obtain positive samples in entire batch
num_pos = []
for cp, bp, ct, bt in zip(
*[cls_pred, box_pred, cls_target, box_target]):
pos_samples = (ct > 0)
num_pos.append(pos_samples.sum())
num_pos_all = sum([p.asscalar() for p in num_pos])
if num_pos_all < 1 and self._min_hard_negatives < 1:
# no positive samples and no hard negatives, return dummy losses
cls_losses = [nd.sum(cp * 0) for cp in cls_pred]
box_losses = [nd.sum(bp * 0) for bp in box_pred]
sum_losses = [
nd.sum(cp * 0) + nd.sum(bp * 0)
for cp, bp in zip(cls_pred, box_pred)
]
return sum_losses, cls_losses, box_losses
cls_losses = []
box_losses = []
sum_losses = []
for cp, bp, ct, bt in zip(
*[cls_pred, box_pred, cls_target, box_target]):
pos = ct > 0
cls_loss = self.focal_loss(cp, ct)
cls_losses.append(cls_loss / max(1., num_pos_all))
bp = nd.reshape_like(bp, bt)
box_loss = nd.abs(bp - bt)
box_loss = nd.where(box_loss > self._rho,
box_loss - 0.5 * self._rho,
(0.5 / self._rho) * nd.square(box_loss))
# box loss only apply to positive samples
box_loss = box_loss * pos.expand_dims(axis=-1)
box_losses.append(
nd.sum(box_loss, axis=0, exclude=True) / max(1., num_pos_all))
sum_losses.append(cls_losses[-1] + self._lambd * box_losses[-1])
return sum_losses, cls_losses, box_losses
def test_reshape_like():
a = nd.array(np.zeros((SMALL_Y, LARGE_X)))
b = nd.array(np.zeros((SMALL_Y//2, LARGE_X*2)))
c = nd.reshape_like(a, b)
assert c.shape == (SMALL_Y//2, LARGE_X*2)