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bode_bounds.m

## Copyright (C) 1996, 2000, 2004, 2005, 2006, 2007
##               Auburn University. All rights reserved.
##
##
## 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 (at
## your option) 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; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{wmin}, @var{wmax}] =} bode_bounds (@var{zer}, @var{pol}, @var{dflg}, @var{tsam})
## Get default range of frequencies based on cutoff frequencies of system
## poles and zeros.
## Frequency range is the interval
## @iftex
## @tex
## $ [ 10^{w_{min}}, 10^{w_{max}} ] $
## @end tex
## @end iftex
## @ifinfo
## [10^@var{wmin}, 10^@var{wmax}]
## @end ifinfo
##
## Used internally in @command{__freqresp__} (@command{bode}, @command{nyquist})
## @end deftypefn

function [wmin, wmax] = bode_bounds (zer, pol, DIGITAL, tsam)

  if (nargin != 4)
    print_usage ();
  endif

  ## make sure zer,pol are row vectors
  if (! isempty (pol))
    pol = reshape (pol, 1, length (pol));
  endif
  if (! isempty (zer))
    zer = reshape (zer, 1, length (zer));
  endif

  if (isa (zer, "single") || isa (pol, "single"))
    myeps = eps ("single");
  else
    myeps = eps;
  endif

  ## check for natural frequencies away from omega = 0
  if (DIGITAL)
    ## The 2nd conditions prevents log(0) in the next log command
    iiz = find (abs(zer-1) > norm(zer)*myeps && abs(zer) > norm(zer)*myeps);
    iip = find (abs(pol-1) > norm(pol)*myeps && abs(pol) > norm(pol)*myeps);

    ## avoid dividing empty matrices, it would work but looks nasty
    if (! isempty (iiz))
      czer = log (zer(iiz))/tsam;
    else
      czer = ;
    endif

    if (! isempty (iip))
      cpol = log (pol(iip))/tsam;
    else
      cpol = ;
    endif
  else
    ## continuous
    iip = find (abs(pol) > norm(pol)*myeps);
    iiz = find (abs(zer) > norm(zer)*myeps);

    if (! isempty (zer))
      czer = zer(iiz);
    else
      czer = ;
    endif
    if (! isempty (pol))
      cpol = pol(iip);
    else
      cpol = ;
    endif
  endif
  
  if (isempty (iip) && isempty (iiz))
    ## no poles/zeros away from omega = 0; pick defaults
    wmin = -1;
    wmax = 3;
  else
    wmin = floor (log10 (min (abs ([cpol, czer]))));
    wmax = ceil (log10 (max (abs ([cpol, czer]))));
  endif

  ## expand to show the entirety of the "interesting" portion of the plot
  wmin--;
  wmax++;

  ## run digital frequency all the way to pi
  if (DIGITAL)
    wmax = log10 (pi/tsam);
  endif

endfunction

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