fzdm(f,a,b,tol,varargin)

function [x,k]= fzdm(f,a,b,tol,varargin)
%   find zero of f(x) by dichotomy in the interval [a  b]
%   f(a)*f(b)<0  by hypothesis
%
%  tol is the stopping criterion
%  varargin is additionnal user parameters of f(x)
%
%  on return
% k is the number of calls of f(x)
% x is the zero of f(x)
%
%  the function f is as follows
%  function fx=f(x,varargin)
%  
%   author Alain barraud   mars 2009
%
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x=(a+b)/2;k=0;
while abs(b-a)>tol*abs(x)+1.e-1*tol
    fx=f(x,varargin{:});k=k+1;
    if fx>0
        b=x;
    elseif fx<0
        a=x;
    else
        a=x;b=x;
    end
    disp(['k, x, fx : ',num2str(k),'    ',num2str([x,fx],'%25.15e')]);
    x=(a+b)/2;
end
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