Grouped Convolution

A Grouped Convolution uses a group of convolutions - multiple kernels per layer - resulting in multiple channel outputs per layer. This leads to wider networks helping a network learn a varied set of low level and high level features. The original motivation of using Grouped Convolutions in AlexNet was to distribute the model over multiple GPUs as an engineering compromise. But later, with models such as ResNeXt, it was shown this module could be used to improve classification accuracy. Specifically by exposing a new dimension through grouped convolutions, cardinality (the size of set of transformations), we can increase accuracy by increasing it.