You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: simplify.m
    path of file: ./repos/chebfun/@separableApprox
    
    the code of the file until where you have to start completion: function f = simplify( f, tol, rank_flag )
% Simplify a SEPARABLEAPPROX
%

    
function f = simplify( f, tol, rank_flag )
% Simplify a SEPARABLEAPPROX
%
% F = SIMPLIFY( F ) compressed the representation of F to one that is
% numerically the same, but requires fewer parameters to store. This
% simplifies the bivariate polynomial degree of F, but not its rank.
%
% F = SIMPLIFY(F, TOL) does the same as SIMPLIFY( F ) but uses the scalar 
% TOL instead of the default simplification tolerance as the relative 
% threshold level for compression.
%
% F = SIMPLIFY(F, 'rank') compressed the rank of the representation for F 
% to one that is numerically the same. 
%
% F = SIMPLIFY(F, TOL, 'rank') does the same as SIMPLIFY(F, 'rank') but 
% uses the scalar TOL instead of the default simplification tolerance as 
% the relative threshold level for compression.

% Copyright 2017 by The University of Oxford and The Chebfun2 Developers.
% See http://www.chebfun.org/ for Chebfun2 information.

simplifyRank = 0;   % do not simplify the rank by default.
if ( nargin < 2 )
    tol = [];
end