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poisson.c
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poisson.c
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#include<stdio.h>
#include<math.h>
void writeGrid(int N, double grid[N][N]){
int i,j;
FILE* fout = fopen("grid.txt", "w");
for(i=0; i<N; ++i){
for(j=0; j<N; ++j){
fprintf(fout, "%30.16g ", grid[i][j]);
}
fprintf(fout, "\n");
}
fclose(fout);
}
void copy(const int N, double from[N][N], double to[N][N]){
int i,j;
for(i=0; i<N; ++i){
for(j=0; j<N; ++j){
to[i][j] = from[i][j];
}
}
}
int main(){
double PI = 3.14159265358979323846;
double dens=0;
//set a delta for the separation inbetwen points
double delta =0.1;
//boundary conditions U(0,y)=U(L,y)=U(x,0)=0 U(x,L)=100 a box
double max=20;
int tamano=max/delta;
printf("\n resta: %8.4d", tamano);
double U[tamano][tamano];
//fullfill the matrix with zeros esta sera mi guess
for(int i=0;i<tamano;i++){
for(int j=0;j<tamano;j++){
U[i][j]=0;
}
}
//mi condicion inicial esto no es exactamente una funcion pero a ver si sirve
for(int i=0;i<tamano;i++){
U[i][0]=100;
}
double oldcopy[tamano][tamano];
double resta[tamano][tamano];
copy(tamano, U, oldcopy);
for(int i=1;i<tamano-1;i++){
for(int j=1;j<tamano-1;j++){
U[i][j]=((U[i+1][j]+U[i-1][j]+U[i][j+1]+U[i][j-1])/4)+PI*dens*pow(delta,2);
resta[i][j]=U[i][j]-oldcopy[i][j];
}
}
printf("\n resta: %8.4f", resta[1][1]);
double maximum = resta[1][1];
int m=tamano, n=tamano;
for (int c = 1; c < m-1; c++){
for (int d = 1; d < n-1; d++){
if (resta[c][d] > maximum){
maximum = resta[c][d];}}}
printf("\n maximum: %8.4f", maximum);
while(maximum>0.01){
copy(tamano, U, oldcopy);
for(int i=1;i<tamano-1;i++){
for(int j=1;j<tamano-1;j++){
U[i][j]=((U[i+1][j]+U[i-1][j]+U[i][j+1]+U[i][j-1])/4)+PI*dens*pow(delta,2);
resta[i][j]=U[i][j]-oldcopy[i][j];
//printf("\n resta: %8.4f", resta[i][j]);
}
}
maximum=resta[0][0];
for (int c = 1; c < m-1; c++){
for (int d = 1; d < n-1; d++){
if (resta[c][d] > maximum){
maximum = resta[c][d];}}}
printf("\n maximum: %8.4f", maximum);
}
//create my mesh
writeGrid(tamano, U);
return 0;
}