今天自定義不可導函數(shù)的時候遇到了一個大坑。
首先我需要自定義一個函數(shù)：sign_f
import torch
from torch.autograd import Function
import torch.nn as nn
class sign_f(Function):
@staticmethod
def forward(ctx, inputs):
output = inputs.new(inputs.size())
output[inputs >= 0.] = 1
output[inputs 0.] = -1
ctx.save_for_backward(inputs)
return output
@staticmethod
def backward(ctx, grad_output):
input_, = ctx.saved_tensors
grad_output[input_>1.] = 0
grad_output[input_-1.] = 0
return grad_output
然后我需要把它封裝為一個module 類型，就像 nn.Conv2d 模塊 封裝 f.conv2d 一樣，于是
import torch
from torch.autograd import Function
import torch.nn as nn
class sign_(nn.Module):
# 我需要的module
def __init__(self, *kargs, **kwargs):
super(sign_, self).__init__(*kargs, **kwargs)
def forward(self, inputs):
# 使用自定義函數(shù)
outs = sign_f(inputs)
return outs
class sign_f(Function):
@staticmethod
def forward(ctx, inputs):
output = inputs.new(inputs.size())
output[inputs >= 0.] = 1
output[inputs 0.] = -1
ctx.save_for_backward(inputs)
return output
@staticmethod
def backward(ctx, grad_output):
input_, = ctx.saved_tensors
grad_output[input_>1.] = 0
grad_output[input_-1.] = 0
return grad_output
結果報錯
TypeError: backward() missing 2 required positional arguments: 'ctx' and 'grad_output'
我試了半天，發(fā)現(xiàn)自定義函數(shù)后面要加 apply ，詳細見下面
import torch
from torch.autograd import Function
import torch.nn as nn
class sign_(nn.Module):
def __init__(self, *kargs, **kwargs):
super(sign_, self).__init__(*kargs, **kwargs)
self.r = sign_f.apply ### -----注意此處
def forward(self, inputs):
outs = self.r(inputs)
return outs
class sign_f(Function):
@staticmethod
def forward(ctx, inputs):
output = inputs.new(inputs.size())
output[inputs >= 0.] = 1
output[inputs 0.] = -1
ctx.save_for_backward(inputs)
return output
@staticmethod
def backward(ctx, grad_output):
input_, = ctx.saved_tensors
grad_output[input_>1.] = 0
grad_output[input_-1.] = 0
return grad_output
問題解決了！
有的時候我們需要給損失函數(shù)設一個超參數(shù)但是又不想設固定閾值想和網(wǎng)絡一起自動學習，例如給Sigmoid一個參數(shù)alpha進行調節(jié)
函數(shù)如下：
import torch.nn as nn
import torch
class LearnableSigmoid(nn.Module):
def __init__(self, ):
super(LearnableSigmoid, self).__init__()
self.weight = torch.nn.Parameter(torch.FloatTensor(1), requires_grad=True)
self.reset_parameters()
def reset_parameters(self):
self.weight.data.fill_(1.0)
def forward(self, input):
return 1/(1 + torch.exp(-self.weight*input))
驗證和Sigmoid的一致性
class LearnableSigmoid(nn.Module):
def __init__(self, ):
super(LearnableSigmoid, self).__init__()
self.weight = torch.nn.Parameter(torch.FloatTensor(1), requires_grad=True)
self.reset_parameters()
def reset_parameters(self):
self.weight.data.fill_(1.0)
def forward(self, input):
return 1/(1 + torch.exp(-self.weight*input))
Sigmoid = nn.Sigmoid()
LearnSigmoid = LearnableSigmoid()
input = torch.tensor([[0.5289, 0.1338, 0.3513],
[0.4379, 0.1828, 0.4629],
[0.4302, 0.1358, 0.4180]])
print(Sigmoid(input))
print(LearnSigmoid(input))
輸出結果
tensor([[0.6292, 0.5334, 0.5869],
[0.6078, 0.5456, 0.6137],
[0.6059, 0.5339, 0.6030]])
tensor([[0.6292, 0.5334, 0.5869],
[0.6078, 0.5456, 0.6137],
[0.6059, 0.5339, 0.6030]], grad_fn=MulBackward0>)
驗證權重是不是會更新
import torch.nn as nn
import torch
import torch.optim as optim
class LearnableSigmoid(nn.Module):
def __init__(self, ):
super(LearnableSigmoid, self).__init__()
self.weight = torch.nn.Parameter(torch.FloatTensor(1), requires_grad=True)
self.reset_parameters()
def reset_parameters(self):
self.weight.data.fill_(1.0)
def forward(self, input):
return 1/(1 + torch.exp(-self.weight*input))
class Net(nn.Module):
def __init__(self):
super(Net, self).__init__()
self.LSigmoid = LearnableSigmoid()
def forward(self, x):
x = self.LSigmoid(x)
return x
net = Net()
print(list(net.parameters()))
optimizer = optim.SGD(net.parameters(), lr=0.01)
learning_rate=0.001
input_data=torch.randn(10,2)
target=torch.FloatTensor(10, 2).random_(8)
criterion = torch.nn.MSELoss(reduce=True, size_average=True)
for i in range(2):
optimizer.zero_grad()
output = net(input_data)
loss = criterion(output, target)
loss.backward()
optimizer.step()
print(list(net.parameters()))
輸出結果
tensor([1.], requires_grad=True)]
[Parameter containing:
tensor([0.9979], requires_grad=True)]
[Parameter containing:
tensor([0.9958], requires_grad=True)]
會更新~
以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。
