specifying Namespace for Matrix class?

I am starting with some of the octave sample code (modified below) calling
octave from C++. I eventually will have another Matrix class in the code so
I need to differentiate by namespace.
  I cannot find out which namespace in octave contains "Matrix" but I
vaguely recall it is in "math". Obviously I am wrong  per this error
message:
     matr.cpp:11:17: error: ‘Matrix’ is not a member of ‘octave::math’
              octave::math::Matrix a_matrix = Matrix (n, n);
Any ideas which namespace it is in so I can qualify it in the code?

Thanks
Fritz

=============CODE=============
#include <iostream>
#include <octave/oct.h>

using namespace octave::math;

int main (void)
{
  std::cout << "Hello Octave world!\n";
  int n = 2;
  octave::math::Matrix a_matrix = Matrix (n, n);
  for (octave_idx_type i = 0; i < n; i++)
    for (octave_idx_type j = 0; j < n; j++)
      a_matrix(i,j) = (i + 1) * 10 + (j + 1);
  std::cout << a_matrix;
  return 0;
}


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