public class Matrices2 {

    public static void main (String[] argv)
    {
        // Make two samples matrices.
	double[][] A = {
	    {1, 3, 5},
	    {7, 9, 11},
	    {13, 15, 17},
        };

	double[][] B = {
	    {1, 0, 0},
	    {0, 1, 0},
	    {0, 0, 1},
	};

        // Addition.
	double[][] C = add (A, B);
	System.out.println ("Sum C = A + B: ");
	print (C);

        // Multiplication.
	double[][] D = multiply (A, B);
	System.out.println ("Product D = A * B: ");
	print (D);

        // Power.
	double[][] E = power (B, 10);
	System.out.println ("Power B^10: ");
	print (E);
    }


    static void print (double[][] X)
    {
	for (int i=0; i<X.length; i++) {
	    for (int j=0; j<X[i].length; j++) {
		System.out.printf (" %4.1f", X[i][j]);
	    }
	    System.out.println ();
	}
    }


    static double[][] add (double[][] X, double[][] Y) 
    {
        // See if the matrices are compatible.
	if ( (X.length != Y.length) || (X[0].length != Y[0].length) ) {
	    System.out.println ("Incompatible matrices");
	    System.exit(0);
	}

        // Create space for the result.
	double[][] Z = new double [X.length][X[0].length];

        // Simple element-by-element addition.
	for (int i=0; i<X.length; i++) {
	    for (int j=0; j<X[i].length; j++) {
		Z[i][j] = X[i][j] + Y[i][j];
	    }
	}

	return Z;
    }


    static double[][] multiply (double[][] X, double[][] Y) 
    {
        // Check that we can multiply.
	if ( (X.length != Y[0].length) && (X[0].length != Y.length) ) {
	    System.out.println ("Incompatible matrices");
	    System.exit(0);
	}

        // Space for result.
	double[][] Z = new double [X.length][Y[0].length];

        // For (i,j)-th element of Z, multiply i-row of X by j-th row of Y.
	for (int i=0; i<Z.length; i++) {
	    for (int j=0; j<Z[i].length; j++) {

                // This is the row x col result.
		double sum = 0;
		for (int k=0; k<X[0].length; k++) {
		    sum += X[i][k] * Y[k][j];
		}

		Z[i][j] = sum;
	    }
	}

	return Z;
    }


    static double[][] power (double[][] X, int n)
    {
    }

}