Mercurial > octave
view scripts/special-matrix/wilkinson.m @ 33570:c978eff7a857 default tip @
maint: Merge stable to default.
author | Markus Mützel <markus.muetzel@gmx.de> |
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date | Sat, 11 May 2024 14:59:27 +0200 |
parents | 2e484f9f1f18 |
children |
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######################################################################## ## ## Copyright (C) 1999-2024 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{W} =} wilkinson (@var{n}) ## Return the Wilkinson matrix of order @var{n}. ## ## Wilkinson matrices are symmetric and tridiagonal with pairs of nearly, but ## not exactly, equal eigenvalues. They are useful in testing the behavior and ## performance of eigenvalue solvers. ## ## @seealso{rosser, eig} ## @end deftypefn function W = wilkinson (n) if (nargin < 1) print_usage (); endif if (! (isscalar (n) && n >= 0 && (n == fix (n)))) error ("wilkinson: N must be a non-negative integer"); endif side = ones (n-1, 1); center = abs (-(n-1)/2:(n-1)/2); W = diag (side, -1) + diag (center) + diag (side, 1); endfunction %!assert (wilkinson (0), []) %!assert (wilkinson (1), 0) %!assert (wilkinson (2), [0.5,1;1,0.5]) %!assert (wilkinson (3), [1,1,0;1,0,1;0,1,1]) %!assert (wilkinson (4), [1.5,1,0,0;1,0.5,1,0;0,1,0.5,1;0,0,1,1.5]) ## Test input validation %!error <Invalid call> wilkinson () %!error <N must be a non-negative integer> wilkinson (ones (2)) %!error <N must be a non-negative integer> wilkinson (-1) %!error <N must be a non-negative integer> wilkinson (1.5)