MOdify the program below to do 3x3 matrix mutiplications: #include <iostream> #i

Question

MOdify the program below to do 3x3 matrix mutiplications:

#include <iostream>

#include <cstdlib>

#include <pthread.h>

using namespace std;

int A[3] [3] = {{1,2},{3,4}};

int B[3] [3] = {{5,6},{7,8}};

int C[3] [3];

struct Position{

    int row;

    int col;

};

void *CalculateElement(void *pos){

    Position *p = (Position *)pos;

    C[p->row][p->col] = 0;

    for(int i = 0; i < 3; i++){

        C[p->row][p->col] += A[p->row][i]*B[i][p->col];

    }

    pthread_exit(NULL);

}

const int NUM_THREADS = 4;

int main()

{

    pthread_t threads[NUM_THREADS];

    for(int i = 0; i < NUM_THREADS; i++){

        Position *p = new Position;

        p->row = i/NUM_THREADS;

        p->col = i%NUM_THREADS;

        pthread_create(&threads[i], NULL, CalculateElement, (void *)p);

    }

   for(int i = 0; i < NUM_THREADS; i++){

        pthread_join(threads[i], NULL);

    }

    cout << "The result matrix is: ";

    for(int i = 0; i < 3; i++){

        for(int j = 0; j < 3; j++){

            cout << C[i][j] << " ";

        }

        cout << endl;

    }

}

Explanation / Answer

Answer for Question:

I have updated the matrix A and B array values 3 x 3 .

Step 1: Update the A and B matrix values with 3 x 3 arrays.

int A[3] [3] = {{1,2,5},{3,4,6},{6,7,8}};
int B[3] [3] = {{5,6,9},{7,8,6},{3,5,8}};

Step 2: Updated Code:

#include <iostream>
#include <cstdlib>
#include <pthread.h>
using namespace std;

int A[3] [3] = {{1,2,5},{3,4,6},{6,7,8}};
int B[3] [3] = {{5,6,9},{7,8,6},{3,5,8}};
int C[3] [3];

struct Position
{
int row;
int col;
};

void *CalculateElement(void *pos){
Position *p = (Position *)pos;
C[p->row][p->col] = 0;
for(int i = 0; i < 3; i++){
C[p->row][p->col] += A[p->row][i]*B[i][p->col];
}
pthread_exit(NULL);
}

const int NUM_THREADS = 4;

int main()
{
pthread_t threads[NUM_THREADS];

for(int i = 0; i < NUM_THREADS; i++){
Position *p = new Position;
p->row = i/NUM_THREADS;
p->col = i%NUM_THREADS;
pthread_create(&threads[i], NULL, CalculateElement, (void *)p);
}

for(int i = 0; i < NUM_THREADS; i++){
pthread_join(threads[i], NULL);
}
cout << "The result matrix is: ";
for(int i = 0; i < 3; i++){
for(int j = 0; j < 3; j++){
cout << C[i][j] << " ";
}
cout << endl;
}
}

Step 3: Output

The result matrix is:

34 47 61

13 0 0

0 0 0

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