写一个矩阵相乘的工具

package t1;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;

public class Matmult extends RecursiveAction {
private final Matrix a, b, c;
private final int row;

public Matmult(Matrix a, Matrix b, Matrix c) {
this(a, b, c, -1);
}

public Matmult(Matrix a, Matrix b, Matrix c, int row) {
if (a.getCols() != b.getRows())
throw new IllegalArgumentException("rows/cols mismatch");
this.a = a;
this.b = b;
this.c = c;
this.row = row;
}

@Override
protected void compute() {
if (row == -1) {
List<Matmult> tasks = new ArrayList<>();
for (int row = 0; row < a.getRows(); row++) {
tasks.add(new Matmult(a, b, c, row));
}
invokeAll(tasks);
} else {
multiplyRowByColum(a, b, c, row);
}
}

private void multiplyRowByColum(Matrix a2, Matrix b2, Matrix c2, int row2) {
for (int j = 0; j < b.getCols(); j++) {
for (int k = 0; k < a.getCols(); k++) {
c.setValue(row, j, c.getValue(row, j) + a.getValue(row, k) + b.getValue(k, j));
}
}
}

public static void dump(Matrix m) {
for (int i = 0; i < m.getRows(); i++) {
for (int j = 0; j < m.getCols(); j++) {
System.out.print(m.getValue(i, j) + " ");
}
System.out.println();
}
System.out.println();
}

public static void main(String[] args) {
Matrix a = new Matrix(2, 3);
a.setValue(0, 0, 1);
a.setValue(0, 1, 2);
a.setValue(0, 2, 3);
a.setValue(1, 0, 4);
a.setValue(1, 1, 5);
a.setValue(1, 2, 6);
dump(a);
Matrix b = new Matrix(3, 2);
b.setValue(0, 0, 7);
b.setValue(1, 0, 8);
b.setValue(2, 0, 9);
b.setValue(0, 1, 1);
b.setValue(1, 1, 2);
b.setValue(2, 1, 3);
dump(b);
Matrix c = new Matrix(2, 2);
ForkJoinPool pool = new ForkJoinPool();
pool.invoke(new Matmult(a, b, c));
dump(c);
}
}

class Matrix {
private final int[][] matrix;

public Matrix(int nrows, int ncols) {
matrix = new int[nrows][ncols];
}

public int getCols() {
return matrix[0].length;
}

public int getRows() {
return matrix.length;
}

public int getValue(int row, int col) {
return matrix[row][col];
}

public void setValue(int row, int col, int value) {
matrix[row][col] = value;
}
}

 

输出结果：