## Copyright (C) 1993, 1994, 1995, 2000, 2002, 2004, 2005, 2006, 2007
##               John W. Eaton
##
## 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.
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## WITHOUT ANY WARRANTY; without even the implied warranty of
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## 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
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} damp (@var{p}, @var{tsam})
## Displays eigenvalues, natural frequencies and damping ratios
## of the eigenvalues of a matrix @var{p} or the @math{A} matrix of a
## system @var{p}, respectively.
## If @var{p} is a system, @var{tsam} must not be specified.
## If @var{p} is a matrix and @var{tsam} is specified, eigenvalues
## of @var{p} are assumed to be in @var{z}-domain.
## @seealso{eig}
## @end deftypefn

## Author: Kai P. Mueller <mueller@ifr.ing.tu-bs.de>
## Created: September 29, 1997.

function damp (p, tsam)

  ## assume a continuous system
  DIGITAL = 0;

  if (nargin < 1 || nargin > 2)
    print_usage ();
  endif

  if (isstruct (p))
    if (nargin != 1)
      error("damp: when p is a system, tsamp parameter is not allowed.");
    endif
    [aa, b, c, d, t_samp] = sys2ss (p);
    DIGITAL = is_digital (p);
  else
    aa = p;
    if (nargin == 2)
      DIGITAL = 1;
      t_samp = tsam;
    endif
  endif
  if (! issquare (aa))
    error ("damp: Matrix p is not square.")
  endif
  if (DIGITAL && t_samp <= 0.0)
    error ("damp: Sampling time tsam must not be <= 0.")
  endif

  ## all checks done.
  e = eig (aa);
  [n, m] = size (aa);
  if (DIGITAL)
    printf ("  (discrete system with sampling time %f)\n", t_samp);
  endif
  printf ("............... Eigenvalue ...........     Damping     Frequency\n");
  printf ("--------[re]---------[im]--------[abs]----------------------[Hz]\n");
  for i = 1:n
    pole = e(i);
    cpole = pole;
    if (DIGITAL)
      cpole = log (pole) / t_samp;
    endif
    d0 = -cos (atan2 (imag (cpole), real (cpole)));
    f0 = 0.5 / pi * abs (cpole);
    if (abs (imag (cpole)) < eps)
      printf ("%12f         ---  %12f  %10f  %12f\n",
             real (pole), abs (pole), d0, f0);
    else
      printf ("%12f %12f %12f  %10f  %12f\n",
             real (pole), imag (pole), abs (pole), d0, f0);
    endif
  endfor

endfunction
