# include <mat2cpp.hpp>
# include <cassert>
namespace mat2cpp {
     double sum 
     (const matrix<double> &x)
     {    double y = 0.;
          size_t m = x.size1();
          size_t n = x.size2();
          size_t i, j;
          for(i = 0; i < m; i++)
          {    for(j = 0; j < n; j++)
                    y += x(i, j);
          }
          return y;
     }
}