parallelizing Mandelbrot using MPI - c

Question

I am trying to parallelize the Mandelbrot.
the correct output should be around 1.510659. however I am not getting that correctly.
** PROGRAM: Mandelbrot area
**
** PURPOSE: Program to compute the area of a Mandelbrot set.
** The correct answer should be around 1.510659.
**
** USAGE: Program runs without input ... just run the executable
**
reduction for numoutside.
this is my parallelized code
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <mpi.h>
#define NPOINTS 1000
#define MAXITER 1000
int P = 1;
struct d_complex
{
double r;
double i;
};
int testpoint(struct d_complex);
struct d_complex c;
struct d_complex cPart;
int numoutside = 1;
int main()
{
int i, j, row;
int res;
double area, error, eps = 1.0e-5;
int myrank, mysize;
double stsec, ensec, commtime, maxcommtime;
MPI_Status status;
MPI_Init(NULL, NULL);
MPI_Comm_size(MPI_COMM_WORLD, &mysize);
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
stsec = MPI_Wtime();
// Loop over grid of points in the complex plane which contains the Mandelbrot set,
// testing each point to see whether it is inside or outside the set.
/*for (i = 0; i < NPOINTS; i ++)
{
for (j = 0; j < NPOINTS ; j++)
{
c.r = -2.0 + 2.5 * (double)(i) / (double)(NPOINTS) + eps;
c.i = 1.125 * (double)(j) / (double)(NPOINTS) + eps;
testpoint(c);
}
}*/
if (myrank == 0)
{
/* Begin User Program - the master */
//*
int outsum, nb_pixel = NPOINTS*NPOINTS ;
for (i = 0; i < nb_pixel; i++)
{
MPI_Recv(&res, 1, MPI_INT, MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &status);
// printf("Slave id %d has send : %d \n", status.MPI_SOURCE, data[2]);
// printf("%d: [%d,%d] -> [%d,%d] = %d\n", status.MPI_SOURCE, data[0], data[1], data[0] + MAXX, data[1] + MAXY, data[2]);
res += numoutside;
}
area = 2.0 * 2.5 * 1.125 * (double)(NPOINTS * NPOINTS - res) / (double)(NPOINTS * NPOINTS);
error = area / (double)NPOINTS;
printf("Area of Mandlebrot set = %12.8f +/- %12.8f\n", area, error);
printf("Finish.\n");
}
else
{
for (i = myrank; i < NPOINTS; i+=mysize)
{
for (j = 0; j < NPOINTS; j++)
{
c.r = -2.0 + 2.5 * (double)(i) / (double)(NPOINTS) + eps;
c.i = 1.125 * (double)(j) / (double)(NPOINTS) + eps;
res=testpoint(c);
MPI_Send(&res, 1, MPI_INT, 0, 0, MPI_COMM_WORLD);
}
}
}
// Calculate area of set and error estimate and output the results
MPI_Finalize();
ensec = MPI_Wtime();
commtime = ensec - stsec;
// area = 2.0 * 2.5 * 1.125 * (double)(NPOINTS * NPOINTS - numoutside) / (double)(NPOINTS * NPOINTS);
// error = area / (double)NPOINTS;
printf("Area of Mandlebrot set = %12.8f +/- %12.8f\n", area, error);
if (myrank == 0)
{
printf("%.3f\n", commtime);
}
}
int testpoint(struct d_complex c)
{
// Does the iteration z=z*z+c, until |z| > 2 when point is known to be outside set
// If loop count reaches MAXITER, point is considered to be inside the set
struct d_complex z;
int iter;
double temp;
z = c;
for (iter = 0; iter < MAXITER; iter++)
{
temp = (z.r * z.r) - (z.i * z.i) + c.r;
z.i = z.r * z.i * 2 + c.i;
z.r = temp;
if ((z.r * z.r + z.i * z.i) > 4.0)
{
// MPI_Send( &numoutside, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD);
return numoutside;
break;
}
}
return 0;
}
the expectation is to get around 1.510659 when running the code with NPOINTS: 1000,2000 and 2,4, processors .