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scripts/general/nthroot.m

changeset 10289: 4b124317dc38
parent:eb63fbe60fab
author: John W. Eaton <jwe@octave.org>
date: Tue Feb 09 20:58:55 2010 -0500 (36 minutes ago)
permissions: -rw-r--r--
description: base_properties::set_children: account for hidden children 
     1## Copyright (C) 2004, 2006, 2007, 2009 Paul Kienzle

     2##

     3## This file is part of Octave.

     4##

     5## Octave is free software; you can redistribute it and/or modify it

     6## under the terms of the GNU General Public License as published by

     7## the Free Software Foundation; either version 3 of the License, or (at

     8## your option) any later version.

     9##

    10## Octave is distributed in the hope that it will be useful, but

    11## WITHOUT ANY WARRANTY; without even the implied warranty of

    12## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    13## General Public License for more details.

    14##

    15## You should have received a copy of the GNU General Public License

    16## along with Octave; see the file COPYING.  If not, see

    17## <http://www.gnu.org/licenses/>.

    18##

    19## Original version by Paul Kienzle distributed as free software in the

    20## public domain.

    21

    22## -*- texinfo -*-

    23## @deftypefn {Function File} {} nthroot (@var{x}, @var{n})

    24## 

    25## Compute the n-th root of @var{x}, returning real results for real 

    26## components of @var{x}.  For example

    27##

    28## @example

    29## @group

    30## nthroot (-1, 3)

    31## @result{} -1

    32## (-1) ^ (1 / 3)

    33## @result{} 0.50000 - 0.86603i

    34## @end group

    35## @end example

    36##

    37## @end deftypefn

    38

    39function y = nthroot (x, m)

    40

    41  if (nargin != 2)

    42    print_usage ();

    43  endif

    44  

    45  y = x.^(1./m);

    46

    47  if (isscalar (x))

    48    x *= ones (size (m)); 

    49  endif

    50

    51  if (isscalar (m))

    52    m *= ones (size (x)); 

    53  endif

    54

    55  idx = (mod (m, 2) == 1 & imag (x) == 0 & x < 0);

    56

    57  if (any (idx(:)))

    58    y(idx) = -(-x(idx)).^(1./m(idx)); 

    59  endif

    60

    61  ## If result is all real, make sure it looks real

    62  if (all (imag (y) == 0))

    63    y = real (y); 

    64  endif

    65

    66endfunction

    67

    68%!assert(nthroot(-1,[3,-3]), [-1,-1],eps);

    69%!assert(nthroot([-1,1],[3.1,-3]), [-1,1].^(1./[3.1,-3]));

    70%!assert(nthroot([-1+1i,-1-1i],3), [-1+1i,-1-1i].^(1/3));