y_x0 = torch.autograd.grad(y, pt_x_in,grad_outputs=torch.ones_like(net(pt_x_in)),create_graph=True)[0]
时间: 2024-05-30 10:16:51 浏览: 269
This line of code computes the gradient of the output tensor 'y' with respect to the input tensor 'pt_x_in' using the backpropagation algorithm.
The 'grad_outputs' argument specifies the initial gradients to be used when computing the gradients of 'y' with respect to its inputs. Here, we set it to a tensor of ones with the same shape as the output of the neural network 'net(pt_x_in)'.
The 'create_graph' argument is set to 'True' to enable the computation of higher-order derivatives in subsequent calculations.
The resulting gradient tensor 'y_x0' will have the same shape as 'pt_x_in' and contains the gradients of 'y' with respect to each element of 'pt_x_in'.
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y_x0 = torch.autograd.grad(y, 0,grad_outputs=torch.ones_like(net(pt_x_in)),create_graph=True)[0]
This line of code computes the gradient of a given function y with respect to its first argument (parameter 0) at a specific input point pt_x_in. The gradient is computed using automatic differentiation provided by PyTorch's autograd module.
The optional argument grad_outputs=torch.ones_like(net(pt_x_in)) specifies the shape and dtype of the initial gradient tensor. In this case, it creates a tensor of ones with the same shape as the output of the neural network net evaluated at pt_x_in.
The create_graph=True argument allows the computation graph to be retained, so that higher-order derivatives can be computed if needed. The resulting gradient tensor is returned as the output of the function.
pt_x_bc_var = Variable(torch.from_numpy(x_bc_var).float(), requires_grad=False) pt_x_in_pos_one = Variable(torch.from_numpy(x_in_pos_one).float(), requires_grad=False) pt_x_in_zeros = Variable(torch.from_numpy(x_in_zeros).float(), requires_grad=False) pt_t_in_var = Variable(torch.from_numpy(t_in_var).float(), requires_grad=False) pt_u_in_zeros = Variable(torch.from_numpy(u_in_zeros).float(), requires_grad=False) # 求边界条件的损失 net_bc_right = net(torch.cat([pt_x_in_zeros, pt_t_in_var], 1)) # u(0,t)的输出 mse_u_2 = mse_cost_function(net_bc_right, pt_u_in_zeros) # e = 0-u(0,t) 公式(2) net_bc_left = net(torch.cat([pt_x_in_pos_one, pt_t_in_var], 1)) # u(1,t)的输出 mse_u_3 = mse_cost_function(net_bc_left, pt_u_in_zeros) x_0 = torch.cat([pt_x_in_zeros, pt_t_in_var], 1) x_1 = torch.cat([pt_x_in_pos_one, pt_t_in_var], 1) pt_x_0 = x_0.detach().requires_grad_(True) pt_x_1 = x_1.detach().requires_grad_(True) net_bc_right.requires_grad_(True) net_bc_left.requires_grad_(True) u_x_0 = torch.autograd.grad(net_bc_right, pt_x_0, grad_outputs=torch.ones_like(net_bc_right), create_graph=True, allow_unused=True)[0][:, 0].unsqueeze(-1) u_x_1 = torch.autograd.grad(net_bc_left, pt_x_1, grad_outputs=torch.ones_like(net_bc_left), create_graph=True, allow_unused=True)[0][:, 0].unsqueeze(-1) u_xx_0 = torch.autograd.grad(u_x_0, pt_x_0, grad_outputs=torch.ones_like(u_x_0), create_graph=True, allow_unused=True)[0][:, 0].unsqueeze(-1) u_xx_1 = torch.autograd.grad(u_x_1, pt_x_1, grad_outputs=torch.ones_like(u_x_1), create_graph=True, allow_unused=True)[0][:, 0].unsqueeze(-1)这串代码有什么问题吗?该怎么解决
这段代码没有明显的语法问题,但是有可能会导致梯度计算的错误,因为在计算 u_x_0, u_x_1, u_xx_0, u_xx_1 的时候,使用了 detach() 方法,这会使得计算图中的某些节点与原来的计算图断开,从而导致梯度无法传递到这些节点,进而影响到 u 的梯度计算。为了解决这个问题,可以使用 retain_graph=True 参数来保留计算图,或者在计算 u_x_0, u_x_1, u_xx_0, u_xx_1 的时候不使用 detach() 方法。
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