examples/research_projects/visual_bert/modeling_frcnn.py/BasicStem/__init__
class BasicStem:    def __init__(self, in_channels=3, out_channels=64, norm="BN", caffe_maxpool=False):
        super().__init__()
        self.conv1 = Conv2d(
            in_channels,
            out_channels,
            kernel_size=7,
            stride=2,
            padding=3,
            bias=False,
            norm=get_norm(norm, out_channels),
        )
        self.caffe_maxpool = caffe_maxpool
        # use pad 1 instead of pad zero