eval.cpp

用内嵌法求多项式

#include <iostream>
#include <math.h>
using namespace std;

double eval(double *,const double &x,const int n);
double horner(double *,double x,int n);
double sqrtt(double b);
main()
{
	double x=1.9887;
	int n=8;
    double a[9]={1,-8,28,-56,70,-56,28,-8,1};
	cout.width(8);
	cout<<eval(a,x,n);
	cout<<endl;
	cout<<horner(a,x,n);
	cout<<endl;
	cout<<pow((x-1),8);
	cout<<endl;
	cout<<sqrtt(12365.147)<<endl;
	cout<<sqrt(12365.147)<<endl;
	return 0;
	

}

double eval(double *a,const double &x,const int n)
{
	double sum=0.0;
	double xpower=0.0;
	for(int i=n;i>=0;i--)
	{    double temp=1;
		//xpower=pow(x,i);
		for(int j=1;j<=i;j++)
		{
		  temp*=x;
		}
		//sum+=a[i]*xpower;
		sum+=a[i]*temp;
	}
	return sum;

}

double horner(double *a,double x,int n)
{
  double u=a[n];
  for(int i=n-1;i>=0;i--)
	  u=u*x+a[i];
  return u;

}

double sqrtt(double b)
{
 double x=1;
 do{
	x=(x+b/x)/2;
 }while(x*x-b>0.00001);

	return x;
}