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: cleanColumns.m
    path of file: ./repos/chebfun/@deltafun
    
    the code of the file until where you have to start completion: function [A, v] = cleanColumns(A, v, pref)
%CLEANCOLUMNS   Remove zero columns from a matrix.
%   [A, V] = CLEANCOLUMNS(A, V) removes impulse columns from A which have all
%   entries negligible and removes the corresponding entry in the vector V. A is
%   typically the matrix of impulses and V is the vector containing locations.
%   This function uses the tolerance provided by CHEBFUNPREF and uses that tolerance 
%   to decide whether a delta function is trivial or not.

    
function [A, v] = cleanColumns(A, v, pref)
%CLEANCOLUMNS   Remove zero columns from a matrix.
%   [A, V] = CLEANCOLUMNS(A, V) removes impulse columns from A which have all
%   entries negligible and removes the corresponding entry in the vector V. A is
%   typically the matrix of impulses and V is the vector containing locations.
%   This function uses the tolerance provided by CHEBFUNPREF and uses that tolerance 
%   to decide whether a delta function is trivial or not.
%
% See also MERGECOLUMNS, MERGEDELTAS, CLEANROWS.

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

% Get the tolerance:
if ( nargin < 3 || isempty(pref) )
    pref = chebfunpref();
end