Mercurial > octave
view scripts/specfun/factor.m @ 29984:c633d34960b4
factor.m: Fix typo in error() message.
* factor.m: Add missing parenthesis ')' to error() message.
author | Rik <rik@octave.org> |
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date | Tue, 17 Aug 2021 16:35:23 -0700 |
parents | ecbcc4647dbe |
children | 39a4ab124fd0 |
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######################################################################## ## ## Copyright (C) 2000-2021 The Octave Project Developers ## ## See the file COPYRIGHT.md in the top-level directory of this ## distribution or <https://octave.org/copyright/>. ## ## This file is part of Octave. ## ## Octave 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. ## ## Octave 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 Octave; see the file COPYING. If not, see ## <https://www.gnu.org/licenses/>. ## ######################################################################## ## -*- texinfo -*- ## @deftypefn {} {@var{pf} =} factor (@var{q}) ## @deftypefnx {} {[@var{pf}, @var{n}] =} factor (@var{q}) ## Return the prime factorization of @var{q}. ## ## The prime factorization is defined as @code{prod (@var{pf}) == @var{q}} ## where every element of @var{pf} is a prime number. If @code{@var{q} == 1}, ## return 1. The output @var{pf} is of the same numeric class as the input. ## ## With two output arguments, return the unique prime factors @var{pf} and ## their multiplicities. That is, ## @code{prod (@var{pf} .^ @var{n}) == @var{q}}. ## ## Implementation Note: The input @var{q} must be less than @code{flintmax} ## when the input is a floating point class (double or single). ## @seealso{gcd, lcm, isprime, primes} ## @end deftypefn function [pf, n] = factor (q) if (nargin < 1) print_usage (); endif if (! isscalar (q) || ! isreal (q) || q < 0 || q != fix (q)) error ("factor: Q must be a real non-negative integer"); endif ## Special case of no primes less than sqrt (q). if (q < 4) pf = q; n = 1; return; endif cls = class (q); # store class if (isfloat (q) && q > flintmax (q)) error ("factor: Q too large to factor (> flintmax)"); endif ## There is at most one prime greater than sqrt(q), and if it exists, ## it has multiplicity 1, so no need to consider any factors greater ## than sqrt(q) directly. [If there were two factors p1, p2 > sqrt(q), ## then q >= p1*p2 > sqrt(q)*sqrt(q) == q. Contradiction.] max_p = feval (cls, sqrt (q)); # restore cls after sqrt conversion to double p = primes (max_p); pf = []; while (q > 1) ## Find prime factors in remaining q. p = p(rem (q, p) == 0); if (isempty (p)) ## Can't be reduced further, so q must itself be a prime. p = q; endif pf = [pf, p]; ## Reduce q. q /= prod (p); endwhile pf = sort (pf); ## Determine multiplicity. if (nargout > 1) idx = find ([0, pf] != [pf, 0]); pf = pf(idx(1:length (idx)-1)); n = diff (idx); endif endfunction ## Test special case input %!assert (factor (1), 1) %!assert (factor (2), 2) %!assert (factor (3), 3) %!test %! for i = 2:20 %! pf = factor (i); %! assert (prod (pf), i); %! assert (all (isprime (pf))); %! [pf, n] = factor (i); %! assert (prod (pf.^n), i); %! assert (all ([0,pf] != [pf,0])); %! endfor %!assert (factor (uint8 (8)), uint8 ([2 2 2])) %!assert (factor (single (8)), single ([2 2 2])) %!test %! [pf, n] = factor (int16 (8)); %! assert (pf, int16 (2)); %! assert (n, double (3)); ## Test input validation %!error <Invalid call> factor () %!error <Q must be a real non-negative integer> factor ([1,2]) %!error <Q must be a real non-negative integer> factor (6i) %!error <Q must be a real non-negative integer> factor (-20) %!error <Q must be a real non-negative integer> factor (1.5) %!error <Q too large to factor> factor (flintmax ("single") + 2) %!error <Q too large to factor> factor (flintmax ("double") + 2)