Multiplying matrices Java

Question

I've been have some problems multiplying the matrices for this code, when I do it by hand and with a calculation tool I get something completely different than what my code is giving me.

Code:

public class mult1 {
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        double[][] colaO = {{.9,0.05,0.05},{0.05,.9,0.05},{0.05,0.05,.9}};//orginal
        double[][] colaD = {{.9,0.05,0.05},{0.05,.9,0.05},{0.05,0.05,.9}};//copy
        double[][] colaC = {{.9,0.05,0.05},{0.05,.9,0.05},{0.05,0.05,.9}};//for algs
        mult1 test = new mult1();
        test.output(colaC);
        test.Alg1(colaO, colaD, colaC);
        test.output(colaC);
    }
    public void Alg1(double colaO[][],double colaD[][],double colaC[][]){
        for(int i=0;i<colaO.length;i++){
            for(int j=0;j<colaO.length;j++){
                for(int k=0;k<colaO.length;k++){
                    colaC[i][j]+=colaO[i][k]*colaD[k][j];
                }
            }
        }
    }
    public void output(double colaC[][]){
        for(int i=0;i<colaC.length;i++){
            for(int j=0;j<colaC.length;j++){
                System.out.printf("%.3f",colaC[i][j]);
                System.out.print(" ");
            }
            System.out.println();
        }
    }
}

Results:

 ---original-----
 0.900 0.050 0.050 
 0.050 0.900 0.050 
 0.050 0.050 0.900 
 ---what i'm getting------
 1.715 0.143 0.143 
 0.143 1.715 0.143 
 0.143 0.143 1.715 
 ---should be-----
 0.815 0.092 0.092
 0.092 0.815 0.092
 0.092 0.092 0.815

I don't quite see where I'm messing up the equation

Answer 1

Well the first thing I would do is 0-initialise colaC since you're using += on its entries. The way you're doing it now can't lead to the correct result.

Answer 2

double[][] colaC = {{.9,0.05,0.05},{0.05,.9,0.05},{0.05,0.05,.9}};//for algs

应该

double[][] colaC = {{0,0,0},{0,0,0},{0,0,0}};//for algs