001    /**
002     * Parallel Matrix Multiplication. 
003     * Using specified number of threads.
004     * @author Heinz Kredel.
005     */
006    
007    public class ParMultProc implements MMInf {
008    
009        int anzahl = 1;
010    
011        public ParMultProc(int threads) {
012             anzahl = threads;      
013        }
014    
015    
016    /**
017     * Performs the multiplication of two matrices.
018     * C = A * B.
019     * @param C result matrix.
020     * @param A matrix.
021     * @param B matrix.
022     */
023        public void multiply(double[][] C, double[][] A, double[][] B) {
024          Thread[] t = new Thread[anzahl];
025          System.out.print("Starting " + anzahl + " threads ...");
026          for (int i=0; i < anzahl; i++) {
027              t[i] = new RowMultProc(C,A,B,i,anzahl);
028              t[i].start();
029          }
030          System.out.print(" started ...");
031          for (int i=0; i < anzahl; i++) {
032              try { t[i].join(); }
033              catch (InterruptedException e) { }
034          }
035          System.out.println(" done ParMultProc");
036        }
037    
038    }
039    
040    
041    /**
042     * This class is derived from the class Thread.
043     * It performs a row multiplication.
044     */
045    class RowMultProc extends Thread {
046    
047        double[][] A;
048        double[][] B;
049        double[][] C;
050        int i;  
051        int anzahl;
052    
053    /**
054     * Constructor.
055     * @param Cp Two dimensional matrices.
056     * @param Ap Two dimensional matrices.
057     * @param Bp Two dimensional matrices.
058     */
059      RowMultProc(double[][] Cp, double[][] Ap, double[][] Bp, int ip, int a) {
060        A = Ap; B = Bp; C = Cp; i = ip; anzahl = a;
061      }
062    
063    /**
064     * Runs the multiplication.
065     */
066      public void run() {
067        int schritte = A.length / anzahl; 
068        if ( (A.length % anzahl) != 0 ) {
069            schritte++; // ceiling
070        }
071        for (int ii = i*schritte; ii < Math.min((i+1)*schritte,A.length); ii++ ) {
072            double[] Ai = A[i];
073            for (int j=0; j < B[0].length; j++) {
074                double c = 0.0;
075                for (int k=0; k < B.length; k++) {
076                     c += A[ii][k] * B[k][j];
077                }
078                C[ii][j] = c;
079            }
080        }
081      }
082    
083    }