Multi-Branch Merge (Inception-style)

The same Inception-style block as the graph style’s multi-branch example - four parallel branches (a plain Conv2d+BatchNorm2d, a 1x1-then-3x3 conv, a 1x1-then-5x5 conv, and a max-pool-then-1x1-conv) that all read the same input and merge into a shared projection layer - rendered in lenet style instead.

Conv2d is orange, BatchNorm2d is green, and MaxPool2d is reddish purple. Shape labels are turned off here (show_dimension=False) since parallel branches share a column, which would otherwise overlap several labels on top of each other.

from collections import defaultdict

import matplotlib.pyplot as plt
import torch
import visualtorch
from torch import nn


class InceptionBlock(nn.Module):
    """A simplified Inception-style block with four parallel branches."""

    def __init__(self, in_channels: int, out_1x1: int, out_3x3: int, out_5x5: int, out_pool: int) -> None:
        super().__init__()
        self.branch1 = nn.Sequential(
            nn.Conv2d(in_channels, out_1x1, kernel_size=1),
            nn.BatchNorm2d(out_1x1),
        )
        self.branch2 = nn.Sequential(
            nn.Conv2d(in_channels, out_3x3, kernel_size=1),
            nn.Conv2d(out_3x3, out_3x3, kernel_size=3, padding=1),
        )
        self.branch3 = nn.Sequential(
            nn.Conv2d(in_channels, out_5x5, kernel_size=1),
            nn.Conv2d(out_5x5, out_5x5, kernel_size=5, padding=2),
        )
        self.branch4 = nn.Sequential(
            nn.MaxPool2d(kernel_size=3, stride=1, padding=1),
            nn.Conv2d(in_channels, out_pool, kernel_size=1),
        )
        total_channels = out_1x1 + out_3x3 + out_5x5 + out_pool
        self.project = nn.Conv2d(total_channels, total_channels, kernel_size=1)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        """Run every branch on the same input, then concatenate and project."""
        b1 = self.branch1(x)
        b2 = self.branch2(x)
        b3 = self.branch3(x)
        b4 = self.branch4(x)
        merged = torch.cat([b1, b2, b3, b4], dim=1)
        return self.project(merged)


model = InceptionBlock(in_channels=16, out_1x1=8, out_3x3=8, out_5x5=8, out_pool=8)

input_shape = (1, 16, 16, 16)

color_map: dict = defaultdict(dict)
color_map[nn.Conv2d]["fill"] = "#E69F00"
color_map[nn.BatchNorm2d]["fill"] = "#009E73"
color_map[nn.MaxPool2d]["fill"] = "#CC79A7"

img = visualtorch.render(model, input_shape, style="lenet", color_map=color_map, scale_xy=1.5, show_dimension=False)

dpi = 150  # rendered at 2x this in the final doc build (savefig.dpi=300 in conf.py)
plt.figure(figsize=(img.width / dpi, img.height / dpi), dpi=dpi)
plt.imshow(img)
plt.axis("off")
plt.tight_layout()
plt.show()