rSCINTROPARALLEL/poisson.c
c8aa63f79c19implementation/c++

poisson.c
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			#include "io_ascii.h"

			#include <math.h>
			#include <stdio.h>
			#include <stdlib.h>

			#define N 256

			int main() {
			int i, j;
			char k;
			float ** u;
			float ** uo;
			float ** f;
			float h;

			h = 1. / (N + 1);

			// Allocation of arrays of pointers (columns)
			u = (float *)malloc((N + 1) sizeof(float *));
			uo = (float *)malloc((N + 1) sizeof(float *));
			f = (float *)malloc((N + 1) sizeof(float *));

			// allocation of the rows
			for (i = 0; i < N + 1; i++) {
			u[i] = (float )malloc((N) sizeof(float));
			uo[i] = (float )malloc((N) sizeof(float));
			f[i] = (float )malloc((N) sizeof(float));
			}

			// initialization of u0 and f
			for (i = 0; i < N + 1; i++) {
			for (j = 0; j < N + 1; j++) {
			u[i][j] = 0;
			uo[i][j] = 0;
			f[i][j] = -2. * 100. * M_PI * M_PI * sin(10. * M_PI * i * h) *
			sin(10. * M_PI * j * h);
			}
			}

			for (k = 0; k < 200; ++k) {
			for (i = 0; i < N; i++) {
			for (j = 0; j < N; j++) {
			// computation of the new step
			u[i][j] = 0.25 * (uo[i - 1][j] + uo[i + 1][j] + uo[i][j - 1] +
			uo[i][j + 1] - f[i][j] * h * h);
			}
			}

			// copy new grid in old grid
			for (i = 0; i < N + 1; i++) {
			for (j = 0; j < N + 1; j++) {
			uo[i][j] = u[i][j];
			}
			}

			write_to_file(N + 1, u, k, -1., 1.);
			}

			// de-allocation of the rows
			for (i = 0; i < N + 1; i++) {
			free(u[i]);
			free(uo[i]);
			free(f[i]);
			}

			return 0;
			}