matrix multiplication

[VeganFanatic]

This does not work as expected, for matrix * matrix matrix operator*(const matrix that) { // matrix product AB != BA matrix ret; ret.resize(this->data.size(), that.data.size()); for (int i = 0; i < this->data.size(); i++) { for (int j = 0; j < this.data[i].size(); j++) { for (int k = 0; k < this->data.size(); k++) { #pragma omp parallel for for (int l = 0; l < this.data[i].size(); l++) { ret[i][k] += this->data[i][k] * that.data[j][k]; } } } } return ret;

http://www.contract-developer.tk

[David Crow]

So what exactly is the question? Have you used the debugger to step through the code? Have you removed the #pragma directive? Have you worked out on paper how to do the multiplication?

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"Man who follows car will be exhausted." - Confucius

[VeganFanatic]

The result from a test != book

http://www.contract-developer.tk

[CPallini]

VeganFanatic wrote:

for (int i = 0; i < this->data.size(); i++) { for (int j = 0; j < this.data[i].size(); j++) { for (int k = 0; k < this->data.size(); k++) { #pragma omp parallel for for (int l = 0; l < this.data[i].size(); l++) { ret[i][k] += this->data[i][k] * that.data[j][k]; } } } }

AFAIK it should be

for (int i = 0; i < this->rows; i++)
for (int j = 0; j < that->cols; j++)
{
ret[i][j] = .0; // assuming your elements are doubles...
for (int k = 0; k < this->cols; k++) //this->cols must be equal to that->rows
ret[i][j] += this->data[i][k] * that.data[k][j];
}

Why do you need the further loop? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]