%function [c,err,yc]=bisect(f,a,b,delta)
function [c,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) 2004 by John H. Mathews and Kurtis D. Fink
%  Complementary Software to accompany the textbook:
%  NUMERICAL METHODS: Using Matlab, Fourth Edition
%  ISBN: 0-13-065248-2
%  Prentice-Hall Pub. Inc.
%  One Lake Street
%  Upper Saddle River, NJ 07458

ya=feval(f,a);
yb=feval(f,b);

if ya*yb > 0
    return
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
        return
    end
end

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