bisect.m

国外计算机科学教材系列 numerial method using matlab (third edition)

function [c,err,yc]=bisect(f,a,b,delta)

%Input - f is the function input as a string 'f'
%	    - a and b are the left and right endpoints
%	    - delta is the tolerance
%Output - c is the zero
%	     - yc= f(c)
% 	     - err is the error estimate for c

% NUMERICAL METHODS: MATLAB Programs
%(c) 1999 by John H. Mathews and Kurtis D. Fink
%To accompany the textbook:
%NUMERICAL METHODS Using MATLAB,
%by John H. Mathews and Kurtis D. Fink
%ISBN 0-13-270042-5, (c) 1999
%PRENTICE HALL, INC.
%Upper Saddle River, NJ 07458

ya=feval(f,a);
yb=feval(f,b);
if ya*yb > 0,break,end
max1=1+round((log(b-a)-log(delta))/log(2));
for k=1:max1
	c=(a+b)/2;
	yc=feval(f,c);
	if yc==0
		a=c;
		b=c;
	elseif yb*yc>0
		b=c;
		yb=yc;
	else
		a=c;
		ya=yc;
	end
	if b-a < delta, break,end
end

c=(a+b)/2;
err=abs(b-a);
yc=feval(f,c);