C++ 嵌套 for 循环 - 内积 - marix 乘法

Question

I have a matrix A with 4 rows and 3 columns and a matrix B with 8 rows and 4 columns. The coefficiants in the first column of B should denote those rows of A that I want to take for the inner product with the rows of B.

#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;

int main()
{
int ik, il, im;
//A Matrix
vector<vector<int>> A(4, vector<int>(3));
A={ {0, 0, 0}, {1, 1, 0}, {0, 0, 1}, {1, 1, 1} };

//B Matrix
vector<vector<int>> B(8, vector<int>(4));
B={ {1, 0, 0, 0}, {2, 1, 0, 0}, {2, 0, 1, 0}, {2, 1, 1, 0} ,{3, 0, 0, 1}, {4, 1, 0, 1}, {4, 0, 1, 1}, {4, 1, 1, 1} };

vector<int> BZI; 
BZI={{1},{2},{2},{2},{3},{4},{4},{4}};

//calculate inner products
vector<vector<int>> SKP_AB(4, vector<int>(8));
int skp_temp;
for(ik=0; ik<4; ik++)
{
  for(im=0; im<8; im++)
  {
    for(il=0; il<3; il++)
    {
    skp_temp=A[BZI[ik]][il]*B[im][il+1];
    SKP_AB[ik][im]+=skp_temp;
    }
  }
}
//Ausgabe von SKP_AB
cout << "\n" << "#SKP_AB" << "\n";
for(ik=0; ik<4; ++ik)
{
 for(il=0; il<8; ++il)
 {
 cout << setw(2) << SKP_AB[ik][il];
 }
cout << "\n";
}

return 0;
}

Answer 1

In both BZI and the first column of B you used one based row indexing, but C++ uses zero based row indexing.

So you need to compensate, where you had BZI[ik] you needed BZI[ik]-1

Notice also how hard it was to reach that answer without being told what output you expected (only your program wasn't working) vs. how obvious it was once told what output you expected.