function [root, ea, iter] = bisection(func,xl,xu,es, maxit, varargin)

test=func(xl,varargin{:})*func(xu,varargin{:})

if test > 0, error, end

if nargin < 4 | isempty(es), es=0.00001;end

if nargin < 5 | isempty(maxit), es=50;end

iter=0; xr=xl;

while(1)

    xrold = xr;

    xr = (xl+xu)/2;

    iter = iter+1

    if xr ~=0, ea = abs((xr-xrold)/xr)*100; end

    test=func(xl,varargin{:})*func(xu,varargin{:})

    if test < 0

        xu = xr;

    elseif test > 0

        xl=xr;

    else

        ea=0

    end

end

root=xr;