Matrix java in a pgm

Matrix.java

public class Matrix

{

              public static double[][] random(int m, int n)

              {

        double[][] C = new double[m][n];

        for (int i = 0; i < m; i++)

            for (int j = 0; j < n; j++)

                C[i][j] = Math.random();

        return C;

    }

               public static double[][] identity(int n)

              {

        double[][] I = new double[n][n];

        for (int i = 0; i < n; i++)

            I[i][i] = 1;

        return I;

    }

    public static double dot(double[] x, double[] y)

   {

        if (x.length != y.length) throw new RuntimeException("Illegal vector dimensions.");

        double sum = 0.0;

        for (int i = 0; i < x.length; i++)

            sum += x[i] * y[i];

        return sum;

    }

                 public static double[][] transpose(double[][] A)

                 {

        int m = A.length;

        int n = A[0].length;

        double[][] C = new double[n][m];

        for (int i = 0; i < m; i++)

            for (int j = 0; j < n; j++)

                C[j][i] = A[i][j];

        return C;

    }

    public static double[][] add(double[][] A, double[][] B)

   {

        int m = A.length;

        int n = A[0].length;

        double[][] C = new double[m][n];

        for (int i = 0; i < m; i++)

            for (int j = 0; j < n; j++)

                C[i][j] = A[i][j] + B[i][j];

        return C;

    }

                 public static double[][] subtract(double[][] A, double[][] B)

                {

        int m = A.length;

        int n = A[0].length;

        double[][] C = new double[m][n];

        for (int i = 0; i < m; i++)

            for (int j = 0; j < n; j++)

                C[i][j] = A[i][j] - B[i][j];

        return C;

    }

    public static double[][] multiply(double[][] A, double[][] B)

    {

        int mA = A.length;

        int nA = A[0].length;

        int mB = B.length;

        int nB = A[0].length;

        if (nA != mB) throw new RuntimeException("Illegal matrix dimensions.");

        double[][] C = new double[mA][nB];

        for (int i = 0; i < mA; i++)

            for (int j = 0; j < nB; j++)

                for (int k = 0; k < nA; k++)

                    C[i][j] += (A[i][k] * B[k][j]);

        return C;

    }

                 public static double[] multiply(double[][] A, double[] x)

                {

        int m = A.length;

        int n = A[0].length;

        if (x.length != n) throw new RuntimeException("Illegal matrix dimensions.");

        double[] y = new double[m];

        for (int i = 0; i < m; i++)

            for (int j = 0; j < n; j++)

                y[i] += (A[i][j] * x[j]);

        return y;

    }

    public static double[] multiply(double[] x, double[][] A)

   {

        int m = A.length;

        int n = A[0].length;

        if (x.length != m) throw new RuntimeException("Illegal matrix dimensions.");

        double[] y = new double[n];

        for (int j = 0; j < n; j++)

            for (int i = 0; i < m; i++)

                y[j] += (A[i][j] * x[i]);

        return y;

    }

                 public static void main(String[] args)

                {

        System.out.println("D");

        System.out.println("--------------------");

        double[][] d = { { 1, 2, 3 }, { 4, 5, 6 }, { 9, 1, 3} };

        StdArrayIO.print(d);

        System.out.println();

        System.out.println("I");

        System.out.println("--------------------");

        double[][] c = Matrix.identity(5);

        StdArrayIO.print(c);

        System.out.println();

        System.out.println("A");

        System.out.println("--------------------");

        double[][] a = Matrix.random(5, 5);

        StdArrayIO.print(a);

        System.out.println();

        System.out.println("A^T");

        System.out.println("--------------------");

        double[][] b = Matrix.transpose(a);

        StdArrayIO.print(b);

        System.out.println();

        System.out.println("A + A^T");

        System.out.println("--------------------");

        double[][] e = Matrix.add(a, b);

        StdArrayIO.print(e);

        System.out.println();

        System.out.println("A * A^T");

        System.out.println("--------------------");

        double[][] f = Matrix.multiply(a, b);

        StdArrayIO.print(f);

        System.out.println();

    }

}