Multiply two matrices : Array « Collections Data Structure « Java

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2. Collections Data Structure
3. Array

Multiply two matrices

     
/**
 * Multiply two matrices.
 * Only defined for int: TODO: rewrite using 1.5 Generics to add 
 * support for long, float, and double.
 * @author Ian F. Darwin, http://www.darwinsys.com/
 * @version $Id: Matrix.java,v 1.4 2004/03/07 02:53:53 ian Exp $
 */
public class Matrix {

  /* Matrix-multiply two arrays together.
   * The arrays MUST be rectangular.
   * @author Tom Christiansen & Nathan Torkington, Perl Cookbook version.
   */
  public static int[][] multiply(int[][] m1, int[][] m2) {
    int m1rows = m1.length;
    int m1cols = m1[0].length;
    int m2rows = m2.length;
    int m2cols = m2[0].length;
    if (m1cols != m2rows)
      throw new IllegalArgumentException("matrices don't match: " + m1cols + " != " + m2rows);
    int[][] result = new int[m1rows][m2cols];

    // multiply
    for (int i=0; i<m1rows; i++)
      for (int j=0; j<m2cols; j++)
        for (int k=0; k<m1cols; k++)
        result[i][j] += m1[i][k] * m2[k][j];

    return result;
  }

  /** Matrix print.
   */
  public static void mprint(int[][] a) {
    int rows = a.length;
    int cols = a[0].length;
    System.out.println("array["+rows+"]["+cols+"] = {");
    for (int i=0; i<rows; i++) {
      System.out.print("{");
      for (int j=0; j<cols; j++)
        System.out.print(" " + a[i][j] + ",");
      System.out.println("},");
    }
    System.out.println(":;");
  }
  public static void main(String[] argv) {
    //+
    int x[][] = {
      { 3, 2, 3 },
      { 5, 9, 8 },
    };
    int y[][] = {
      { 4, 7 },
      { 9, 3 },
      { 8, 1 },
    };
    int z[][] = Matrix.multiply(x, y);
    Matrix.mprint(x);
    Matrix.mprint(y);
    Matrix.mprint(z);
    //-
  }
}
           
         
    
    
    
    
  

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