Parallelize a Function using openMP in C - c

Question

I wrote a program which inputs matrix size and number of threads and then generated a random binary matrix of 0's and 1's. Then I need to find clusters of 1's and give each cluster a unique number.
I am getting the output correctly but I am having a problem parallelizing the function.
My professor asked me to break the matrix rows into "thread_cnt" parts. i.e.: thread size is 4 and matrix size is 8 then it breaks into 4 matrices having 2 rows each.
The code is as follows:
//Inputted Matrix size n and generated a binary matrix rand1[][]
//
begin = omp_get_wtime();
width = n/thread_cnt;
#pragma omp parallel num_threads(thread_cnt) for
for(d=0;d<n;d=d++)
{
b=d+width;
Mat(d,b);
d=(d-1)+width;
}
Mat(int w,int x)
{
//printf("\n Entered function\n");
for(i=w;i<x;i++)
{
for(j=0;j<n;j++)
{
//printf("\n Entered the loop also\n");
//printf("i = %d, j = %d\n",i,j);
if(rand1[i][j]==1)
{
rand1[i][j]=q;
adj(i,j,q);
q++;
}
}
}
}
adj(int p, int e, int m) //Function to find adjacent 1's
{
//printf("\n Entered adj function\n");
//printf("\n p = %d e = %d m = %d\n",p,e,m);
if (rand1[p][e+1] == 1)
{
//printf("Test1\n");
rand1[p][e+1]=m;
adj(p,e+1,m);
}
if (rand1[p+1][e] == 1)
{
rand1[p+1][e]=m;
//printf("Test2\n");
adj(p+1,e,m);
}
if (rand1[p][e-1] == 1 && e-1>=0)
{
rand1[p][e-1]=m;
//printf("Test3\n");
adj(p,e-1,m);
}
if (p-1>=0 && rand1[p-1][e] == 1)
{
rand1[p-1][e]=m;
//printf("Test4\n");
adj(p-1,e,m);
}
}
The code gives me correct output. But the time increases instead of decreasing when I increase the number of threads. For 1 thread I get 0.000076 and for 2 threads I get
0.000136.
It looks like its iterating instead of parallelizing.
Can anyone help me out on this?
PS: I need to show both Serial time and parallel time and show that I have got a performance increase because of parallelization.

Answer 1

The reason why time increases when thread number increases is that each thread is executing the first loop. It seems that, you don't give the submatrixes into threads, instead each threads operates on every submatrix i.e all matrix.
To make threads work on matrix seperately you should use their unique tid number which you can get with this line :
tid = omp_get_thread_num();
Then you should make a simple mapping : if pid is i operate on (i+1)th submatrix where 0<=i<=nthreads-1
Which can possibly be coded as:
Mat(i*width,i*width+width)