Encounter the RuntimeError: one of the variables needed for gradient computation has been modified b

Encounter the RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation

这句话含义是：梯度计算所需的变量之一在后向传播时已被操作修改。

原因：对变量的赋值是就地操作，比如：

a = torch.rand(2,5,5，requires_grad=True) 
b = torch.rand(2,5,5)
a[:] = a/b  #这一步，使a值重新改变,后向传播时无法更新前向计算的梯度。

正确写法是先复制a_copy=a，再对a_copy进行操作。

a = torch.rand(2,5,5，requires_grad=True) 
b = torch.rand(2,5,5)
a_copy = a
a_copy[:] = a/b