public static double[][] sub( double[][] mat1, double[][] mat2 )
{
	int m = mat1.length;
	int n = mat1[0].length;
	double[][] matres = new double[m][];
	for ( int i = 0; i < m; ++i )
	{
		matres[i] = new double[n];
		for ( int j = 0; j < n; ++j )
			matres[i][j] = mat1[i][j] - mat2[i][j];
	}
	return(matres);
}