弦截法初探

#include"stdio.h"#include"stdlib.h"#include"math.h"float min=0.000001,n=-5555;int a,b,c,d;double yy(double x){return(a*x*x*x+b*x*x+c*x+d);}double xpoint(double x1,double x2){//double x=(x1*yy(x2)-x2*yy(x1))/(yy(x2)-yy(x1));//求(x1,y1)与(x2,y2)两点连成的弦与x轴的交点的x的值int i=0;//if(yy(x1)*yy(x2)>0) return -5001; while(fabs(yy(x1))>min){   if(fabs(x1-x2)<=min) break; if(yy((x1+x2)/2)*(yy(x1))>0)//yy((x1+x2)/2)和y1同号  x1=(x1+x2)/2; else x2=(x1+x2)/2;  //  if(i++%40==0) //printf("x1_%llf  x2_%llf  yy(x1)_%llf\n",x1,x2,yy(x1)); } if(fabs(yy(x1))<=min&&(fabs(x1-n)>min)){n=x1; printf("x=%llf\n",x1);return x1;}else return 5001; }int main(){double x1=-5000.0,x2=-5005.0,x3=5000.0;double add=0.1;printf("请按照aX^3+bX^2+cX^+d=0的形式以a,b,c,d样式输入:\n");scanf("%d,%d,%d,%d",&a,&b,&c,&d);while(x2<x3){xpoint(x1,x2+min);x1+=add;x2+=add;}system("pause");}