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: renameVar.m
    path of file: ./repos/DeepCO3/Lib/matconvnet-1.0-beta24/+dagnn/@DagNN
    
    the code of the file until where you have to start completion: function renameVar(obj, oldName, newName, varargin)
%RENAMEVAR Rename a variable
%   RENAMEVAR(OLDNAME, NEWNAME) changes the name of the variable
%   OLDNAME into NEWNAME. NEWNAME should not be the name of an
%   existing variable.

opts.quiet = false ;
opts = vl_argparse(opts, varargin) ;

% Find the variable to rename
v = obj.getVarIndex(oldName) ;
if isnan(v)

    
function renameVar(obj, oldName, newName, varargin)
%RENAMEVAR Rename a variable
%   RENAMEVAR(OLDNAME, NEWNAME) changes the name of the variable
%   OLDNAME into NEWNAME. NEWNAME should not be the name of an
%   existing variable.

opts.quiet = false ;
opts = vl_argparse(opts, varargin) ;

% Find the variable to rename
v = obj.getVarIndex(oldName) ;
if isnan(v)
  % There is no such a variable, nothing to do
  if ~opts.quiet
    warning('There is no variable ''%s''.', oldName) ;
  end