CODEWITHSUNDEEP
c++matrix
frushan
frushan

Reputation: 21

Matrix multiplying method gives out additional column filled with zeros

I wrote a method that multiplies matrices. It works fine, but gives additional column of zeros. The result of multiplying is correct. Here is the code of method: 

Matrix Matrix::multiplyMatrix(Matrix second)
{

        vector<vector<double> > sum(vec.size(), vector<double> (vec[0].size()));

    if (vec[0].size()!=second.vec.size())
    {
        throw "Dimensions are not correct";
    }
    else 
    {
    for (int i=0; i<vec.size(); i++)
    {
        for (int j=0; j<second.vec[0].size(); j++)
        {
        sum[i][j]=0;
        for (int k=0; k<vec[0].size(); k++)
        {
            sum[i][j]+=vec[i][k]*second.vec[k][j];
        }
    }
    }

    Matrix out(vec.size(), vec[0].size());
    out.vec=sum;
    return out;
    }
}

From main:

Matrix A("A.txt",3,4);
Matrix B("B.txt",4,3);

auto C=A.multiplyMatrix(B);
C.write("C.txt");

Matrices:

A:

2 3 4 4
1 2 4 6
1 1 0 1

and

B:
1 2 3
5 6 7
9 1 5
4 5 5

Instead of 3x3 matrix it gives:

69 46 67 0  
71 48 67 0  
10 13 15 0

Do you know what is the problem? Thanks

Upvotes: 0

Views: 38

Answers (1)

ygy
ygy

Reputation: 124

Your matrix named "out" has the wrong dimensions, also, int the first line of your code, the sum has wrong dimensions too.

the first line should change to:

vector<vector<double> > sum(vec.size(), vector<double> (second.vec[0].size()));

the definition of out should change to:

Matrix out(vec.size(), second.vec[0].size());

Upvotes: 1

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