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: topological_order.m
    path of file: ./repos/CBIG/external_packages/matlab/default_packages/matlab_bgl_mac64
    
    the code of the file until where you have to start completion: function perm=topological_order(A,varargin)
% TOPOLOGICAL_ORDER Returns the topological ordering of vertices in a dag
%

    
function perm=topological_order(A,varargin)
% TOPOLOGICAL_ORDER Returns the topological ordering of vertices in a dag
%
% perm=topological_order(A) generates a permutation of the vertices that
% indices a topological order.  A topological order satisfies the property
% that edge (i,j) in A implies i comes before j in the order.  A
% topological order only exists for directed acyclic graphs.  If A is not a
% directed acyclic graph, then the returned perm is empty.
%
% This method works on directed graphs.
% The runtime is O(V+E).
%
% ... = topological_order(A,...) takes a set of
% key-value pairs or an options structure.  See set_matlab_bgl_options
% for the standard options. 
%   There are no additional options for this function.
%
% Note: this function does not depend