next_pytharogian_triangles.cpp

#include <xtensor/xtensor.hpp>
#include <xtensor-blas/xlinalg.hpp>

xt::xarray<int> next_pytharogian_triples(xt::xarray<int> const& previous_stage)
{
   static const xt::xarray<int> stacked_matrices = {
      { -1, 2, 2 },
      { -2, 1, 2 },
      { -2, 2, 3 },
      { 1, 2, 2 },
      { 2, 1, 2 },
      { 2, 2, 3 },
      { 1, -2, 2 },
      { 2, -1, 2 },
      { 2, -2, 3 }
   };

   auto shape = previous_stage.shape();
   xt::xarray<int> next_three = xt::transpose(xt::linalg::dot(stacked_matrices, xt::transpose(previous_stage)));
   next_three.reshape({ 3 * shape[0], shape[1] });
   return next_three;
}