function L=noshearlength(Ls,a,M,lt)
%NOSHEARLENGTH Transform length that does not require a frequency shear
% Usage: L=noshearlength(Ls,a,M,lt)
%
% NOSHEARLENGTH(Ls,a,M,lt) computes the next larger transform length
% bigger or equal to Ls for which the shear algorithm does not require
% a frequency side shear for a non-separable Gabor system specified by
% a, M and lt.
%
% This property makes computation of the canonical dual and tight Gabor
% windows GABDUAL and GABTIGHT and the DGT for a full length window
% faster, if this transform length is choosen.
%
% See also: matrix2latticetype, dgt, gabdual, gabtight
%
% Url: http://ltfat.github.io/doc/gabor/noshearlength.html
% Copyright (C) 2005-2023 Peter L. Soendergaard <peter@sonderport.dk> and others.
% This file is part of LTFAT version 2.6.0
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program. If not, see <http://www.gnu.org/licenses/>.
Lmin=dgtlength(1,a,M,lt);
if lt(1)==0
Lsmallest=Lmin;
else
c=gcd(a,M);
% if lt(1)>0 then ks is everything in c which is relatively prime to
% lt(2)
kmax=c;
while 1
z=gcd(kmax,lt(2));
if z==1
break;
end;
kmax=kmax/z;
end;
Lsmallest=Lmin*c./kmax;
end;
L=ceil(Ls/Lsmallest)*Lsmallest;