essai04.c

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#include <math.h>
#include <string.h>

#include "mesh1D.h"
#include "quad.h"
#include "utils.h"

void usage(){
  printf("NAME\n\tessai04 - see TP3.pdf\n");
  printf("SYNOPSIS\n\tessai04 [FILENAME] [NINI PAS NFIN]\n");
  printf("DESCRIPTION\n");
  printf("\tFILENAME (optional) : name of the output filename\n");
  printf("\tNINI PAS NFIN (optional) : three integers values\n");
}

double f(double x){
   return 8.*sqrt(x*(1-x)); 
}

void GetMainParameters(int argc,char **argv, 
                       char **pFileName,int *pini,int *ppas,int *pfin);

void ComputeErrors(double (*pf)(double), double a, double b, double Exact,
                   int nini, int pas, int nfin,
                   double **ph, double **pError, int *n);


int main(int argc, char **argv){
  int nini=100,pas=100,nfin=1000; /* default values*/
  char *FileName="";   /* default value*/
  double *ph,*pError;
  int n;
  
  GetMainParameters(argc,argv,&FileName,&nini,&pas,&nfin);
  ComputeErrors(sin,0.,M_PI,2,nini,pas,nfin,&ph,&pError,&n);
  /* Student question : what happens when using the following call of ComputeErrors function
   * instead of the previous one? 
  *    ComputeErrors(f,0.,1.,2.,nini,pas,nfin,&ph,&pError,&n);  */  
  
  if (strlen(FileName)>0){
    printf("Save results in file %s ... \n",FileName);
    saveTwoDoubleDynArray(ph,pError,n,FileName,"%.16e %.16e");
    printf("done.\n");
  }
  Free(ph);
  Free(pError);
  return EXIT_SUCCESS; // return 0
}

void GetMainParameters(int argc,char **argv, 
                       char **pFileName,int *pnini,int *ppas,int *pnfin){
  switch(argc){
    case 1:
      break;
    case 2:
      *pFileName=argv[1];
      break;
    case 5:
      *pFileName=argv[1];
      *pnini=atoi(argv[2]);
      *ppas=atoi(argv[3]);
      *pnfin=atoi(argv[4]);
      break;
    default :
      usage();
      exit(EXIT_FAILURE);
  }
  if (strcmp(*pFileName,"help")==0){
    usage();
    exit(EXIT_FAILURE);
  }
}

void ComputeErrors(double (*pf)(double), double a, double b, double Exact,
                   int nini, int pas, int nfin,
                   double **ph, double **pError,int *pn){
  int nb,i,N;
  double val;
  *pn=(nfin-nini)/pas+1;
  *ph=(double *)Malloc((*pn)*sizeof(double));
  *pError=(double *)Malloc((*pn)*sizeof(double));
  for (i=0;i<*pn;i++) 
    (*pError)[i]=(*ph)[i]=1.0*i;
  for (i=0;i<*pn;i++){
    N=nini+i*pas;
    val=quadPMAlloc(pf,a,b,N,&(*ph)[i]); /* Question for students : What is the difference beetween &(*ph)[i] and ph[i]? */
    (*pError)[i]=fabs(val-Exact)/Exact;
    printf("N=%8d, val=%.16lf, error=%.16e\n",N,val,(*pError)[i]);
  }
}