9sim2.c

一个关于二维积分的c语言程序。很有用 的

#include "math.h"
 double sim2(a,b,eps,ss,f)
 double a,b,eps,(*f)();
 void (*ss)();
 { double simp1();
   int n,j;
   double h,d,s1,s2,t1,x,t2,g,s,s0,ep;
   n=1;h=0.5*(b-a);
   d=fabs((b-a)*1.0e-06);
   s1=simp1(a,eps,ss,f);s2=simp1(b,eps,ss,f);
   t1=h*(s1+s2);
   s0=1.0e+35;ep=1.0+eps;
   while(((ep>=eps)&&(fabs(h)>d))||(n<16))
    { x=a-h;t2=0.5*t1;
     for (j=1;j<=n;j++)
     { x=x+2.0*h;
       g=simp1(x,eps,ss,f);
       t2=t2+h*g;
     }
     s=(4.0*t2-t1)/3.0;
     ep=fabs(s-s0)/(1.0+fabs(s));
     n=n+n;s0=s;t1=t2;h=h*0.5;
    }
    return(s);
 }
   static double simp1(x,eps,s,f)
   double x,eps,(*f)();
   void (*s)();
    { int n,i;
      double y[2],h,d,t1,yy,t2,g,ep,g0;
      n=1;
      (*s)(x,y);
      h=0.5*(y[1]-y[0]);
      d=fabs(h*2.0e-06);
      t1=h*((*f)(x,y[0])+(*f)(x,y[1]));
      ep=1.0+eps;g0=1.0e+35;
      while(((ep>=eps)&&(fabs(h)>d))||(n<16))
	{ yy=y[0]-h;
	  t2=0.5*t1;
	  for (i=1;i<=n;i++)
	   { yy=yy+2.0*h;
	   t2=t2+h*(*f)(x,yy);
	   }
	  g=(4.0*t2-t1)/3.0;
	  ep=fabs(g-g0)/(1.0+fabs(g));
	  n=n+n;g0=g;t1=t2;h=0.5*h;
      }
      return(g);
}