数值分析中的定积分求pi

# include <math.h>
# include <stdio.h>
# define L 9
double f(double x)
{
    return 1.0/(1.0+x*x);
}
double fc(double a,double b,double (*f)())
{
    int m,n,i,k;
    double y[L],h,ep,p,x,s,q;
    h=b-a;
    y[0]=h*((*f)(a)+(*f)(b))/2.0;
    m=1;n=1;ep=1.0;
    while((ep>=1e-10)||(m<=L)){
        p=0.0;
        for(i=0;i<=n-1;i++){
            x=a+(i+0.5)*h;
            p+=(*f)(x);
        }
        p=(y[0]+h*p)/2.0;
        s=1.0;
        for(k=1;k<=m;k++){
            s*=4.0;
            q=(s*p-y[k-1])/(s-1.0);
            y[k-1]=p;p=q;
        }
        ep=fabs(q-y[m-1]);
        m+=1;
        y[m-1]=q;
        n+=n;
        h/=2.0;
    }
    return q;
}
main()
{
    double a,b,t;
    a=0.0;b=1.0;
    t=fc(a,b,f);
    printf("π=3.14159265358979323\n");
    printf("   %.15f",t*4.0);
    getch();
}
 

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