Please consider to use and contribute to Boost.uBlas<https://github.com/boostorg/ublas> which recently added tensor data types and operations with the convenient Einstein notation :
tensor_t C = C + A(_i,_j,_k)*B(_j,_l,_i,_m) + 5;
Thank you Cem for the suggestion! uBlas::opencl definitely looks interesting, since many basic NN layers can be implemented using various element-wise functions, and the hardware support that comes with it is very appealing. The Einstein tensor notation is convenient for multi-dimensional convolution and pooling layers, although I feel that C++ 17 requirement for tensor extension is probably too strong. I will need to experiment with the library a bit more to get a better sense of what it means to implement NN abstractions on top of it. Best regards, Sergei Marchenko.