simp.c

来自「数值分析算法描述与习题解答」· C语言 代码 · 共 44 行

#include "stdio.h"
   #include "math.h"
  main()
  { double a,b,eps,t,simp(),simpf();
    a=0.0; b=1.0; eps=0.000001;
    t=simp(a,b,eps,simpf);
    printf("\n");
    printf("t=%e\n",t);
    printf("\n");
  }

 
  double simpf(x)
   double x;
  {double y;
    y=log(1.0+x)/(1.0+x*x);
    return(y);
  }


 
  double simp(a,b,eps,f)
    double a,b,eps,(*f)();
  { int n,k;
    double h,t1,t2,s1,s2,ep,p,x;
    n=1; h=b-a;
    t1=h*((*f)(a)+(*f)(b))/2.0;
    s1=t1;
    ep=eps+1.0;
    while (ep>=eps)
      { p=0.0;
        for (k=0;k<=n-1;k++)
          { x=a+(k+0.5)*h;
            p=p+(*f)(x);
          }
        t2=(t1+h*p)/2.0;
        s2=(4.0*t2-t1)/3.0;
        ep=fabs(s2-s1);
        t1=t2; s1=s2; n=n+n; h=h/2.0;
      }
    return(s2);
  }