使用指针将c中的矩阵相乘 [英] Multiplying matrices in c using pointers

问题描述

当我输入两个矩阵时，结果矩阵没有显示正确答案，是我的算法错误还是我不应该以这种方式使用指针?请帮忙！

When I input both the matrices, the resultant matrix doesn't show the proper answer, is my algorithm wrong or I am not supposed to use pointers in that way? Please help!

main() {

    int a[3][3],b[3][3],c[3][3],*p[3],*q[3],*r[3],j1=0;

    // 1st Matrix

    for(int i=0;i<3;i++){
        for(int j=0;j<3;j++){
            scanf("%d",&a[i][j]);
        }
    }

    // 2nd matrix

    for(int i=0;i<3;i++){
        for(int j=0;j<3;j++){
            scanf("%d",&b[i][j]);
        }
    }

    // Assigning pointers

    for(int i=0;i<3;i++) p[i]=&a[i][0];
    for(int i=0;i<3;i++) q[i]=&b[i][0];
    for(int i=0;i<3;i++) r[i]=&c[i][0];

    // Resultant Matrix

    for(int i=0;i<3;i++){
        *(*(r+i)+j1) = 0;
        for(j1=0;j1<3;j1++){
            printf("%d\t",*(*(r+i)+j1));
             *(*(r+i)+j1) += *(*(p+i)+j1) * *(*(q+j1)+i);
        }
        j1 = 0;
    }

    for(int i=0;i<3;i++){
        for(int j=0;j<3;j++){
            printf("%d\t",c[i][j]);
        }
        printf("\n");
    }
}

推荐答案

您的循环遍历二维并执行数组 a 和 b 的逐元素乘法与 b 转置.我怀疑您想要执行矩阵乘法而不是逐元素乘法.为此，您需要三个循环:

Your loops iterate through two dimensions and perform an element-wise multiplication of the arrays a and b with b transposed. I suspect you want to perform a matrix multiplication rather than an element-wise multiplication. To do that, you need three loops:

• 两个循环通过 c 的行和列迭代索引 i 和 j.
• 一个循环通过a和b的公共维度迭代某个变量，比如k，并对a的乘积求和[i][k] 和 b[k][j].

• Two loops iterate indices i and j through the rows and columns of c.
• One loop iterates some variable, say k, through the common dimension of a and b and sums the products of a[i][k] with b[k][j].

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