palm_factorial.m

function lfac = palm_factorial(N)
% Computes the log(factorial(0:N)), so dealing with
% precision issues.
%
% lfac = palm_factorial(N)
%
% _____________________________________
% Anderson M. Winkler
% FMRIB / University of Oxford
% Dec/2012
% http://brainder.org

% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
% PALM -- Permutation Analysis of Linear Models
% Copyright (C) 2015 Anderson M. Winkler
% 
% 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
% 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/>.
% - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

persistent lf;
if isempty(lf) || length(lf) < N+1,
    lf = zeros(N+1,1);
    for n = 1:N,
        lf(n+1) = log(n) + lf(n);
    end
end
lfac = lf;