Matrix.java

package org.adi.advanced.matrix;

import java.util.Random;

/******************************************************************************
 *  Compilation:  javac Matrix.java
 *  Execution:    java Matrix
 *
 *  A bare-bones collection of static methods for manipulating
 *  matrices.
 *
 ******************************************************************************/

/*

Input : mat[][] = {{1, 2, 3}, 
                  {4, 5, 6}, 
                  {7, 8, 9}}
Output : Row-wise: 1 2 3 4 5 6 7 8 9
         Col-wise : 1 4 7 2 5 8 3 6 9




*/
public class Matrix {

    // return a random m-by-n matrix with values between 0 and 1
    public static double[][] random(int m, int n) {
        double[][] a = new double[m][n];
        Random random = new Random();
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                a[i][j] = random.nextFloat();
        return a;
    }

    // return n-by-n identity matrix I
    public static double[][] identity(int n) {
        double[][] a = new double[n][n];
        for (int i = 0; i < n; i++)
            a[i][i] = 1;
        return a;
    }

    // return x^T y
    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;
    }

    // return B = A^T
    public static double[][] transpose(double[][] a) {
        int m = a.length;
        int n = a[0].length;
        double[][] b = new double[n][m];
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                b[j][i] = a[i][j];
        return b;
    }

    // return c = a + b
    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;
    }

    // return c = a - b
    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;
    }

    // return c = a * b
    public static double[][] multiply(double[][] a, double[][] b) {
        int m1 = a.length;
        int n1 = a[0].length;
        int m2 = b.length;
        int n2 = b[0].length;
        if (n1 != m2) throw new RuntimeException("Illegal matrix dimensions.");
        double[][] c = new double[m1][n2];
        for (int i = 0; i < m1; i++)
            for (int j = 0; j < n2; j++)
                for (int k = 0; k < n1; k++)
                    c[i][j] += a[i][k] * b[k][j];
        return c;
    }

    // matrix-vector multiplication (y = A * x)
    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]; // result
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                y[i] += a[i][j] * x[j];
        return y;
    }


    // vector-matrix multiplication (y = x^T A)
    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 String toCSV(String[] array) {
        String result = "";

        if (array.length > 0) {
            StringBuilder sb = new StringBuilder();

            for (String s : array) {
                sb.append(s).append(",");
            }

            result = sb.deleteCharAt(sb.length() - 1).toString();
        }
        return result;
}

 public String toMatrixMarket(NumberFormat formatter) {
        StringBuilder out = new StringBuilder();

        out.append("%%MatrixMarket matrix array real general\n");
        out.append(rows).append(' ').append(columns).append('\n');
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < columns; j++) {
                out.append(formatter.format(get(i, j))).append('\n');
            }
        }

        return out.toString();
    }

 static void printMatrix(int[][] matrix) {
        for (int[] line : matrix) {
            int i = 0;
            StringBuilder sb = new StringBuilder(matrix.length);
            for (int number : line) {
                if (i != 0) {
                    sb.append("\t");
                } else {
                    i++;
                }
                sb.append(number);
            }
            System.out.println(sb.toString());
        }
    }
	
	
static void printMatrix(Matrix matrix, int n) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (j != 0) {
                    System.out.print("\t");
                }
                System.out.printf("%.0f", matrix.get(i, j));
            }
            System.out.println("");
        }
    }
	
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
}