The forward two-dimensional (2D) locally-connected layer computes the value tensor Y by applying a set of nKernels 2D kernels K of size m 1 x m 2 to the input argument x. The library supports four-dimensional input tensors XR n 1 x n 2 x n 3 x n 4 . Therefore, the following formula applies:

where i + a < n 1, j + b < n 2, and r is the kernel index.

A set of kernels is specific to the selected dimensions of the input argument x.

See [GregorLecun2010] for additional details of the two-dimensional locally-connected layer.

Problem Statement

Without loss of generality let's assume that convolution kernels are applied to the last two dimensions.

Given:

  • Four-dimensional tensor XR n 1 x n 2 x n 3 x n 4 with input data

  • Six-dimensional tensor KR nKernels x l 3 x l 4 x m 2 x m 3 x m 4 with kernel parameters/weights

  • Three-dimensional tensor BR nKernels x l 3 x l 4 with the bias of each kernel.

For the above tensors:

  • and p i is the respective padding.

  • nGroups is defined as follows: let's assume that n 2 is the group dimension. The input tensor is split along this dimension into nGroups groups, the tensors of values and weights are split into nGroups groups along the nKernels dimension. nKernels and n 2 must be multiples of nGroups. Each group of values is computed using the respective group in tensors of input data, weights, and biases.

The problem is to compute the four-dimensional tensor of values YR n 1 x nKernels x l 3 x l 4 such that:

where:

  • s 3 and s 4 are strides

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