How to define model

User-defined models can be anything derived from torch.nn.Module. For example, we can define a convolutional neural network (CNN) as follows:

User-defined convolutionsl neural network model: examples/models/cnn.py

import torch
import torch.nn as nn
import math

class CNN(nn.Module):
    def __init__(self, num_channel, num_classes, num_pixel):
        super().__init__()
        self.conv1 = nn.Conv2d(
            num_channel, 32, kernel_size=5, padding=0, stride=1, bias=True
        )
        self.conv2 = nn.Conv2d(32, 64, kernel_size=5, padding=0, stride=1, bias=True)
        self.maxpool = nn.MaxPool2d(kernel_size=(2, 2))
        self.act = nn.ReLU(inplace=True)

        ###
        ### X_out = floor{ 1 + (X_in + 2*padding - dilation*(kernel_size-1) - 1)/stride }
        ###
        X = num_pixel
        X = math.floor(1 + (X + 2 * 0 - 1 * (5 - 1) - 1) / 1)
        X = X / 2
        X = math.floor(1 + (X + 2 * 0 - 1 * (5 - 1) - 1) / 1)
        X = X / 2
        X = int(X)

        self.fc1 = nn.Linear(64 * X * X, 512)
        self.fc2 = nn.Linear(512, num_classes)

    def forward(self, x):
        x = self.act(self.conv1(x))
        x = self.maxpool(x)
        x = self.act(self.conv2(x))
        x = self.maxpool(x)
        x = torch.flatten(x, 1)
        x = self.act(self.fc1(x))
        x = self.fc2(x)
        return x

In the code, one can create the CNN model and the loss function instances as follows:

model = CNN()
loss_fn = torch.nn.CrossEntropyLoss()

Note that the loss_fn can be anything derived from torch.nn.Module as well.