golddis.cpp

运筹学中牛顿法和黄金分割法一位搜索的算法C++实现

#include <iostream.h>
#include <math.h>
float f(float t);
float goldcompute(float a,float b,float e);
void main()
{
	float a,b,e,solution;
	cout<<"the desiny function is -2*t*t*t+21*t*t-60*t+50"<<endl
		<<"please input the a and b in (a,b)";
	cin>>a>>b;
	cout<<"please input the value of precision:";
	cin>>e;
	solution=goldcompute(a,b,e);
	cout<<"solution is:"<<solution<<endl;
	cout<<"f(x)="<<f(solution)<<endl
		<<"end";
}
float f(float t)
{
	return -2*t*t*t+21*t*t-60*t+50;
}
float goldcompute(float a,float b,float e)
{
	float t1,t2,f1,f2;
	t1=a+0.382*(b-a); cout<<"t1:"<<t1<<endl;
	t2=a+0.618*(b-a); cout<<"t2:"<<t2<<endl;
	f1=f(t1); cout<<f1<<endl;
	f2=f(t2); cout<<f2<<endl;
	for (;;)
	{
		if(f1<=f2)
		{
          if (t2-a<=e)
		  return t1;
		  else 
		  {
			b=t2; 
			t2=t1;
			t1=b-0.618*(b-a); 
			f2=f1;
			f1=f(t1);
		  }
		}
		else
		{
		  if(b-t1<=e)
		  return t2;
		  else
		  {
			a=t1; 
			t1=t2; 
			t2=a+0.618*(b-a);  
			f1=f2;
			f2=f(t2); 
		  }
		}
	}
}