火炬LSTMCell方法

Question

self.conv1 = nn.Conv2d(num_inputs, 32, 3, stride=2, padding=1)
self.conv2 = nn.Conv2d(32, 32, 3, stride=2, padding=1)
self.conv3 = nn.Conv2d(32, 32, 3, stride=2, padding=1)
self.conv4 = nn.Conv2d(32, 32, 3, stride=2, padding=1)
self.lstm = nn.LSTMCell(32 * 3 * 3, 256)

有人可以提供计算lstm输入的公式（32 * 3 * 3）。这3是哪里来的。