from torch import nn
import torch

class SPP(nn.Module):
    def __init__(self):
        super(SPP, self).__init__()
        self.pool1 = nn.MaxPool2d(kernel_size=5,stride=1,padding=5 // 2)
        self.pool2 = nn.MaxPool2d(kernel_size=7, stride=1, padding=7 // 2)
        self.pool3 = nn.MaxPool2d(kernel_size=13, stride=1, padding=13 // 2)

    def forward(self,x):
        x1 = self.pool1(x)
        x2 = self.pool2(x)
        x3 = self.pool3(x)
        return torch.cat([x,x1,x2,x3],dim=1)

x = torch.rand((2,512,13,13))
f = SPP()
print(f(x).shape)