solver.java

一个期货的类, 可以自由拓展

package edu.nyu.cims.hw4;
import edu.nyu.cims.hw4.IFunction;

public class Solver {
	/**
	 * This method can be used to solve the equation f(x) = 0. We use the 
	 * divide and concur approach. The solver takes a range where to look for solution.
	 * the function at the ends of the range should take opposite signs. We stop
	 * refining the solution once we found a point such that |f(x)| is smaller
	 * than some tolerance.
	 * @param f The function we need to solve.
	 * @param x0 The left boundary in the range where we will look for the solution.
	 * @param x1 The right boundary in the range where we will look for the solution.
	 * @param tolerance The tolerance for the stopping condition.
	 * @return The value x that solves the equation.
	 * @throws Exception If an error occured in the process.
	 */
	public static double findZero(IFunction f, double x0, double x1, double tolerance ) throws Exception{
		// if the function value at x0 or x1 is zero we will return that value.
		if ( f.value(x0) == 0 ){ return x0; }
		if ( f.value(x1) == 0 ){ return x1; }
		// checking that the function takes opposite signs at x0 and x1
		if ( Math.signum( f.value( x0 ) ) == Math.signum( f.value( x1 ) ) ){
			throw new Exception("The function must take opposite signs at x0 and x1." );
		}
		// Setting some variables.
		double left = x0;
		double right = x1;
		double fright = f.value( right );
		double middle = 0.5 * (left + right);
		double fmiddle = f.value( middle );
		while ( Math.abs( fmiddle ) > tolerance ){
			// cutting the range by half.
			if ( Math.signum( fmiddle ) == Math.signum( fright) ){
				right = middle;
				fright = fmiddle;
			} else {
				left = middle;
			}
			// calculating the new middle and f middle.
			middle = 0.5 * (left + right );
			fmiddle = f.value( middle );
		}
		return middle;
	}
	
	
	/*public static void main(String[] args) throws Exception{
		// Suppose we want to solve the equation x^2 = 36 (solution 6).
		IFunction f = new IFunction(){
			public double value(double x) throws Exception {
				return x * x - 36;
			}
			
		};
		System.out.println("Solution: " + findZero(f, 0, 11.56, 1e-6) );
		System.out.println("Solution: " + findZero(f, -100, 0, 1e-6) );
	}*/

}