/*

*

* Jacobi iteration to solve -u'' = 1

*

* parallelize using OpenMP

*

* Yuan-Xun Bao

* April 20, 2015

*

*/

#include <stdio.h>

#include <stdlib.h>

#include <math.h>

#include <omp.h>

#include "util.h"

int main (int argc, char *argv[]){

int N, i, j;

double h, h2, f, r, r0, tol, rt;

double *u, *unew;

int MAX_ITER;

if (argc != 3){

fprintf(stderr, "must input discretization size N and # of iterations\n");

exit(0);

}

N = atoi( argv[1] );

MAX_ITER = atoi( argv[2] );

h = 1./(N+1); h2 = h*h;

f = 1.;

// allocate u, unew

u = (double *) malloc( (N+2) * sizeof(double));

unew = (double *) malloc( (N+2) * sizeof(double));

// fill arrays

for(j = 0; j<=N+1; j++){

u[j] = 0.;

unew[j] = 0.;

}

/*

// initial residual

r0 = 0.0;

for(j=1; j<=N; j++){

rt = (-u[j-1] + 2.*u[j] - u[j+1]) / h2 - f;

r0 += rt*rt;

}

r0 = sqrt(r0/N);

*/

#pragma omp parallel

{

printf("Hello, I am thread %d of %d\n",

omp_get_thread_num(),

omp_get_num_threads());

}

timestamp_type start_t, stop_t;

get_timestamp(&start_t);

/*

r = r0;

while (r/r0 > tol){

*/

for(i = 0; i < MAX_ITER; i++ ){

#pragma omp parallel for default(none) \

schedule(static) \

shared(u,unew,h2,f,N)

//jacobi iteration

for(j= 1; j <=N ; j++){

unew[j] = (h2*f + u[j-1] + u[j+1] ) * 0.5;

}

// printf("Thread %d done\n", omp_get_thread_num());

#pragma omp parallel for default(none) \

schedule(static) \

shared(u,unew,h2,f,N)

// copy work

for(j= 1; j <=N ; j++){

u[j] = unew[j];

}

/*

r = 0.0;

// compute residual

for(j=1; j <= N ; j++){

rt = (-u[j-1] + 2.*u[j] - u[j+1]) / h2 - f;

r = r + rt*rt;

}

r = sqrt(r/N);

*/

// printf("the residual at %dth iteration is %.14f\n", i+1, r);

}

get_timestamp(&stop_t);

double elapsed = timestamp_diff_in_seconds(start_t, stop_t);

printf("Total number of iterations is %d\n", MAX_ITER);

printf("Time elapsed is %f seconds.\n", elapsed);

// printf("the residual at %dth iteration is %.14f\n", MAX_ITER, r);

free(u); free(unew);

return 0;

}