public class MyMatrix {
    //double[][] A = { { 4.00, 3.00 }, { 2.00, 1.00 } };
    //double[][] B = { { -0.500, 1.500 }, { 1.000, -2.0000 } };

    public static double[][] multiplicar(double[][] A, double[][] B) {

        int aRows = A.length;
        int aColumns = A[0].length;
        int bRows = B.length;
        int bColumns = B[0].length;

        if (aColumns != bRows) {
            throw new IllegalArgumentException("A:Rows: " + aColumns + " did not match B:Columns " + bRows + ".");
        }

        

        double[][] C = new double[aRows][bColumns];
        for (int i = 0; i < aRows; i++) {
            for (int j = 0; j < bColumns; j++) {
                C[i][j] = 0.00000;
            }
        }

        for (int i = 0; i < aRows; i++) { // aRow
            for (int j = 0; j < bColumns; j++) { // bColumn
                for (int k = 0; k < aColumns; k++) { // aColumn
                    C[i][j] += A[i][k] * B[k][j];
                }
            }
        }

        return C;
    }

    public static void main(String[] args) {
	final int size=1000;
        long t0, t1;
        double[][] A = new double[size][size];
        double[][] B = new double[size][size];
	for (int i = 0; i < size; i++) {
	    for (int j = 0; j < size; j++) { // fill in some data
                A[i][j] = 0.5 + i+j;
                B[i][j] = 0.5 + j-i;
            }
        }

        for (int k = 0 ; k < 3 ; k++) {
            t0 = System.nanoTime();
            double[][] result = multiplicar(A, B);
            t1 = System.nanoTime() - t0;
            System.out.println("Matrix multiply: no invert, size: " + size + " x " + size + 
                " time: " + t1/1000000000.0 + " s, per element : " + 1.0*t1/size/size/size +
                " ns");
        };
    }
}