pex10_8.cpp

数据结构C++代码,经典代码,受益多多,希望大家多多支持

#include <iostream.h>
#pragma hdrstop

// use the bisection method to approximate a root of
// function f that lies between a and b. terminate
// when an exact root is found or (b-a) < precision 
double Bisect(double f(double x),
			  double a,double b, double precision)
{
	// m is the midpoint of the interval a <= x <= b
	double m = (a+b)/2.0;
	
	// if m is an exact root, return (stopping condition)
	if (f(m) == 0.0)
		return m;
	// if (b-a) < precision, return (stopping condition)
	else if (b-a < precision)
		return m;
	// if the root is in the left half of the interval [a,b],
	// call Bisect for a <= x <= m (recursive step)
	else if (f(a)*f(m) < 0.0)
		return Bisect(f,a,m,precision);
	// if the root is in the right half of the interval [a,b],
	// call Bisect for m <= x <= b (recursive step)
	else
		return Bisect(f,m,b,precision);
}

// function f(x) for which roots are desired
double f(double x)
{
	return x*x*x - 2.0*x - 3.0;
}


// return the balance after paying simple interest on a given
// principal with monthy interest for nmonths
double Balance(double principal, double interest, int nmonths, double payment)
{	
	// subtract interest from the payment. use this amount to
	// reduce the principal. do this for nmonths
	for(int i=1;i <= nmonths;i++)
		principal -= payment - principal*interest;
	return principal;
}

// use Balance to compute the amount owing on a
// $150000 loan at 10% per year for 25 years. the
// payment is x dollars per month
double SpeficBalance(double x)
{
	// interest per month = .10/12,
	// number of payments = 25*12
	return Balance(150000.0,.10/12.0,25*12,x);
}

void main(void)
{
	// approximate the root of f(x) that lies between 1 and 2. use
	// precision = 1.0e-8
	cout << "Root of x*x*x - 2*x - 3 between 1 and 2 is approximately "
		 << Bisect(f,1.0,2.0,1.0e-8) << endl;
		 
	// set precision for dollars and cents
	cout.precision(2);
	cout.setf(ios::showpoint);
	cout.setf(ios::fixed);
	
	// find the root of SpecificBalance between the payments of .01 and 150000
	cout << "Payment on the loan is $"
		 << Bisect(SpeficBalance,.01,150000.0,1.0e-4) << endl;
}

/*
<Run>

Root of x*x*x - 2*x - 3 between 1 and 2 is approximately 1.893289
Payment on the loan is $1363.05
*/