龙贝格积分.c

极有用的数据处理程序

#define PI 3.14159265359
#include<stdio.h>
#include<math.h>
main()
{ 
	double a,b,e;
   double lbgjf(double a,double b,double e);
   printf("input the band(a-->b):");
    scanf("%lf%lf",&a,&b);
   printf("input the precision e:");
       scanf("%lf",&e);
     lbgjf(a,b,e);
}


double lbgjf(double a,double b,double e)
{ 
	double f(double x);
   double d,h,n;
   double T[81];
   int i,j,k,c;
   FILE *file;

   file = fopen( "output.txt", "w" );
   h=b-a;
   T[0]=(f(a)+f(b))*h/2;
   n=0.5;
   for(i=1;i<=10;i++)
   {
	   h=h/2;
	   n=2*n;
	   T[i]=0;
     for(k=1;k<=(int)n;k++)
       T[i]=T[i]+f(a+2*k*h-h);
     T[i]=T[i-1]/2+T[i]*h;
     c=4;
     for(j=1;j<=i;j++)
	 { 
		 d=(T[i+1-j]-T[i-j])/(c-1);
       T[i-j]=T[i+1-j]+d;
	   c=4*c;
	   while(fabs(d)<e)
	   {printf("i=%d,T[%d]=%f\t",i,i-j,T[i-j]);
        fprintf(file,"i=%d",i);
        for(k=0;k<=(i-j);k++)
         fprintf(file,"%16.12f",T[k]);
	   return 0;}
	 }
    fprintf(file,"i=%d",i);
    for(k=1;k<=i;k++)
	{  
		fprintf(file,"%16.12f",T[k]);
    //fprintf(file,"%c",'\n');
	} 
	fprintf(file,"%c",'\n');
   }
   if(fabs(d)>=e)
   {printf("fail!/n");
   printf("T[0]=%f/n",T[0]);
   fprintf(file,"Fail!T[0]=%f/n",T[0]);}
   return 0;
 }

double f(double x)
{double r;
/*if(x==0)
r=1;
else*/
  r=log(1+x)/x;
	  return r;
}