pytorch初步

Install

conda install pytorch torchvision -c soumith

Import

import torch

Tutorial

http://pytorch.org/tutorials/beginner/blitz/tensor_tutorial.html

http://pytorch.org/tutorials/

x = torch.Tensor(5, 3)
print(x)

1.00000e-44 *
  0.0000  0.0000  0.0000
  0.0000  1.6816  0.0000
  0.0000  0.0000  0.0000
  0.0000  0.0000  0.0000
  0.0000  0.0000  0.0000
[torch.FloatTensor of size 5x3]

nn module

http://pytorch.org/tutorials/beginner/pytorch_with_examples.html#nn-module

import torch
from torch.autograd import Variable

# N is batch size; D_in is input dimension;
# H is hidden dimension; D_out is output dimension.
N, D_in, H, D_out = 64, 1000, 100, 10

# Create random Tensors to hold inputs and outputs, and wrap them in Variables.
x = Variable(torch.randn(N, D_in))
y = Variable(torch.randn(N, D_out), requires_grad=False)

# Use the nn package to define our model as a sequence of layers. nn.Sequential
# is a Module which contains other Modules, and applies them in sequence to
# produce its output. Each Linear Module computes output from input using a
# linear function, and holds internal Variables for its weight and bias.
model = torch.nn.Sequential(
    torch.nn.Linear(D_in, H),
    torch.nn.ReLU(),
    torch.nn.Linear(H, D_out),
)

# The nn package also contains definitions of popular loss functions; in this
# case we will use Mean Squared Error (MSE) as our loss function.
loss_fn = torch.nn.MSELoss(size_average=False)

learning_rate = 1e-4
for t in range(500):
    # Forward pass: compute predicted y by passing x to the model. Module objects
    # override the __call__ operator so you can call them like functions. When
    # doing so you pass a Variable of input data to the Module and it produces
    # a Variable of output data.
    y_pred = model(x)

    # Compute and print loss. We pass Variables containing the predicted and true
    # values of y, and the loss function returns a Variable containing the
    # loss.
    loss = loss_fn(y_pred, y)
    if t%50 == 0:
        print(t, loss.data[0])

    # Zero the gradients before running the backward pass.
    model.zero_grad()

    # Backward pass: compute gradient of the loss with respect to all the learnable
    # parameters of the model. Internally, the parameters of each Module are stored
    # in Variables with requires_grad=True, so this call will compute gradients for
    # all learnable parameters in the model.
    loss.backward()

    # Update the weights using gradient descent. Each parameter is a Variable, so
    # we can access its data and gradients like we did before.
    for param in model.parameters():
        param.data -= learning_rate * param.grad.data

(0, 717.2719116210938)
(50, 35.097198486328125)
(100, 1.8821511268615723)
(150, 0.1728428155183792)
(200, 0.02194761298596859)
(250, 0.0034840735606849194)
(300, 0.0006572074489668012)
(350, 0.00014404028479475528)
(400, 3.580378324841149e-05)
(450, 9.810625670070294e-06)

Note