i know this is a false postion method code would the question mark be func(es) ?

function [xr ea iter] = falsepos(func, x1, xu, es, maxit)
% function [xr ea iter] = falsepos(func, x1, xu, es, maxit)
if func(x1)*func(xu)>=0, error('no sign shange'); end 
xold = x1;
for iter=1:maxit
  fl = func(xl);
  fu = func(xu);
  xr = ????