Question

我正在尝试以下列方式实现Strassen的矩阵乘法（一些变量在类的顶部声明，但你知道它们是什么）：

     public double[][] multiplyStrassen(double[][] m, double[][] m2) {
        int n = m.length;

         double [][] result = new double[n][n];
         System.out.println("n = " + n);
        if(n == 1) {
            result[0][0] = m[0][0] * m2[0][0];

        } else {
            A11 = new double[n/2][n/2];
            A12 = new double[n/2][n/2];
            A21 = new double[n/2][n/2];
            A22 = new double[n/2][n/2];

            B11 = new double[n/2][n/2];
            B12 = new double[n/2][n/2];
            B21 = new double[n/2][n/2];
            B22 = new double[n/2][n/2];

            partitionMatrices(m, A11, 0 , 0);
            partitionMatrices(m, A12, 0 , n/2);
            partitionMatrices(m, A21, n/2, 0);
            partitionMatrices(m, A22, n/2, n/2);

            partitionMatrices(m2, B11, 0 , 0);
            partitionMatrices(m2, B12, 0 , n/2);
            partitionMatrices(m2, B21, n/2, 0);
            partitionMatrices(m2, B22, n/2, n/2);

            P1 = multiplyStrassen(addMatrices(A11, A22), addMatrices(B11, B22));
            P2 = multiplyStrassen(addMatrices(A21, A22), B11);
            P3 = multiplyStrassen(A11, subMatrices(B12, B22));
            P4 = multiplyStrassen(A22, subMatrices(B21, B11));
            P5 = multiplyStrassen(addMatrices(A11, A12), B22);
            P6 = multiplyStrassen(subMatrices(A21, A11), addMatrices(B11, B12));
            P7 = multiplyStrassen(subMatrices(A12, A22), addMatrices(B21, B22));

            C11 = addMatrices(subMatrices(addMatrices(P1, P4), P5), P7);
            C12 = addMatrices(P3, P5);
            C21 = addMatrices(P2, P4);
            C22 = addMatrices(subMatrices(addMatrices(P1, P3), P2), P6);

            copyMatrix(C11, result, 0 , 0);
            copyMatrix(C12, result, 0 , n/2);
            copyMatrix(C21, result, n/2, 0);
            copyMatrix(C22, result, n/2, n/2);
        }

        return result;
    }

    public void partitionMatrices(double[][] firstM, double[][] secondM, int A, int B) {
        for(int i1 = 0, i2 = A; i1 < secondM.length; i1++, i2++){
            for(int j1 = 0, j2 = B; j1 < secondM.length; j1++, j2++){
                secondM[i1][j1] = firstM[i2][j2];
            }
        }
    }
    public double[][] addMatrices(double[][] m1, double[][] m2) {
        int n = m1.length;
        double [][] result = new double[n][n];
        System.out.println("Printing m1: ");
        printGrid(m1.length, m1.length);
        System.out.println("Printing m2: ");
        printGrid(m2.length, m2.length);
        for(int i = 0; i < n; i++){
            for(int j = 0; j < n; j++){
                System.out.println("m1[i][j] = " + m1[i][j]);
                System.out.println("m2[i][j] = " + m2[i][j]);
                result[i][j] = m1[i][j] + m2[i][j];
            }
        }
        return result;
    }


    public double [][] subMatrices(double [][] m1, double [][] m2) {
        int n = m1.length;

        double [][] result = new double[n][n];

        for(int i = 0; i < n; i++)
            for(int j = 0; j < n; j++)
                result[i][j] = m1[i][j] - m2[i][j];

        return result;
    }

    public static void copyMatrix(double[][] firstM, double[][] secondM, int A, int B) {
        for(int i1 = 0, i2 = A; i1 < firstM.length; i1++, i2++){
            for(int j1 = 0, j2 = B; j1 < firstM.length; j1++, j2++){
                secondM[i2][j2] = firstM[i1][j1];
            }
        }
    }

编译器抛出：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
   at Matrix.addMatrices(Matrix.java:142)
   at Matrix.multiplyStrassen(Matrix.java:114)
   at MatrixMultiplicationTest.main(MatrixMultiplicationTest.java:20)

我知道这些行号不会为你加起来，因为我在该课程中有其他代码，但我不知道自己哪里出错了，因为我只是在实施算法。代码几乎全部运行，但最终似乎只是破解了。我很感激我能得到的任何帮助。

Answer 1

由于错误显示ArrayIndexOutOfBoundsException：1，因此应该在某个地方尝试从零大小的数组中获取值。它可能来自表达式：

int n = m.length;

double [][] result = new double[n][n];

如果n变为零，则导致初始化零大小的数组。

使用Strassen的矩阵乘法时索引超出范围的异常

1 个答案: