Dive-into-DL-PyTorch
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3.6节train_ch3函数loss计算和sgd问题
bug描述 3.6节train_ch3函数,如果传入的loss已经是求过平均的,train_l_sum每次只累加一个batch的平均值,最后却除以总样本数,打印的loss结果就会很小,例如3.9节的调用。
如果每个batch不一样大(例如Fashion-MNIST设置batch_size=256时,最后一个batch是96),当optimizer=None时,默认的sgd传入batch_size应该会在最后一个batch造成误差,似乎应该使用y.shape[0]。
另外train_ch5是用batch_count,如果batch大小不一致,最后打印的loss也应该会有微小误差。
def train_ch3(net, train_iter, test_iter, loss, num_epochs, batch_size,
params=None, lr=None, optimizer=None):
for epoch in range(num_epochs):
train_l_sum, train_acc_sum, n = 0.0, 0.0, 0
for X, y in train_iter:
y_hat = net(X)
l = loss(y_hat, y).sum()
# 梯度清零
if optimizer is not None:
optimizer.zero_grad()
elif params is not None and params[0].grad is not None:
for param in params:
param.grad.data.zero_()
l.backward()
if optimizer is None:
sgd(params, lr, batch_size)
else:
optimizer.step() # “softmax回归的简洁实现”一节将用到
train_l_sum += l.item()
train_acc_sum += (y_hat.argmax(dim=1) == y).sum().item()
n += y.shape[0]
test_acc = evaluate_accuracy(test_iter, net)
print('epoch %d, loss %.4f, train acc %.3f, test acc %.3f'
% (epoch + 1, train_l_sum / n, train_acc_sum / n, test_acc))
版本信息 pytorch: torchvision: torchtext: ...
你好,我在这个部分出现了下面的error,请问应该怎么修正,有点无从下手
RuntimeError Traceback (most recent call last)
RuntimeError: The size of tensor a (10) must match the size of tensor b (3) at non-singleton dimension 1