For

Contract 2 tensors over head/tail modes and accumulate into result using a custom element-wise multiply-add op The contraction is done via a GEMM operation with fused indices as defined by gemm_config.

Template Parameters

Result	The result tile type
Left	The left-hand tile type
Right	The right-hand tile type
ElementMultiplyAddOp	a callable type with signature void (Result::value_type& result, Left::value_type const& left, Right::value_type const& right) that implements custom multiply-add operation: result = (result) ? result add left mult right : left mult add

Parameters

result	The contracted result; this can be null, will be initialized as needed
left	The left-hand argument to be contracted
right	The right-hand argument to be contracted
gemm_config	A helper object used to simplify gemm operations
element_multiplyadd_op	a custom multiply op operation for tensor elements

Returns

A tile whose element result[i,j] obtained by executing foreach k: element_multiplyadd_op(result[i,j], left[i,k], right[k,j]) plain tensors GEMM can be implemented (very inefficiently) using this method as follows:

gemm(result, left, right, gemm_config,
     [factor](auto& result, const auto& left, const auto& right) {
  result += scalar * (left * right)
});