PyTorch - How To Deactivate Dropout In Evaluation Mode

This is the model I defined it is a simple lstm with 2 fully connect layers. import copy import torch import torch.nn as nn import torch.nn.functional as F import torch.optim as op

Solution 1:

You have to define your nn.Dropout layer in your __init__ and assign it to your model to be responsive for calling eval().

So changing your model like this should work for you:

class mylstm(nn.Module):
    def __init__(self,input_dim, output_dim, hidden_dim,linear_dim,p):
        super(mylstm, self).__init__()
        self.hidden_dim=hidden_dim
        self.lstm=nn.LSTMCell(input_dim,self.hidden_dim)
        self.linear1=nn.Linear(hidden_dim,linear_dim)
        self.linear2=nn.Linear(linear_dim,output_dim)

        # define dropout layer in __init__
        self.drop_layer = nn.Dropout(p=p)
    def forward(self, input):
        out,_= self.lstm(input)

        # apply model dropout, responsive to eval()
        out= self.drop_layer(out)
        out= self.linear1(out)

        # apply model dropout, responsive to eval()
        out= self.drop_layer(out)
        out= self.linear2(out)
        return out

If you change it like this dropout will be inactive as soon as you call eval().

NOTE: If you want to continue training afterwards you need to call train() on your model to leave evaluation mode.

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You can also find a small working example for dropout with eval() for evaluation mode here: nn.Dropout vs. F.dropout pyTorch

Solution 2:

I add this answer just because I'm facing now the same issue while trying to reproduce Deep Bayesian active learning through dropout disagreement. If you need to keep dropout active (for example to bootstrap a set of different predictions for the same test instances) you just need to leave the model in training mode, there is no need to define your own dropout layer.

Since in pytorch you need to define your own prediction function, you can just add a parameter to it like this:

def predict_class(model, test_instance, active_dropout=False):
    if active_dropout:
        model.train()
    else:
        model.eval()

Solution 3:

As the other answers said, the dropout layer is desired to be defined in your model's __init__ method, so that your model can keep track of all information of each pre-defined layer. When the model's state is changed, it would notify all layers and do some relevant work. For instance, while calling model.eval() your model would deactivate the dropout layers but directly pass all activations. In general, if you wanna deactivate your dropout layers, you'd better define the dropout layers in __init__ method using nn.Dropout module.