## Copyright (C) 1996, 1998, 2000 Auburn University.  All rights reserved.
##
## 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 2, or (at your option) any
## later version.
##
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## 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, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301 USA.

## -*- texinfo -*-
## @deftypefn {Function File} {[@var{mag}, @var{phase}, @var{w}] =} bode (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx})
## If no output arguments are given: produce Bode plots of a system; otherwise,
## compute the frequency response of a system data structure
##
## @strong{Inputs}
## @table @var
## @item   sys
## a system data structure (must be either purely continuous or discrete;
## see is_digital)
## @item   w
## frequency values for evaluation.
##
## if @var{sys} is continuous, then bode evaluates @math{G(jw)} where
## @math{G(s)} is the system transfer function.
##
## if @var{sys} is discrete, then bode evaluates G(@code{exp}(jwT)), where
## @itemize @bullet
## @item @math{T} is the system sampling time
## @item @math{G(z)} is the system transfer function.
## @end itemize
##
## @strong{Default} the default frequency range is selected as follows: (These
## steps are @strong{not} performed if @var{w} is specified)
## @enumerate
## @item via routine __bodquist__, isolate all poles and zeros away from
## @var{w}=0 (@var{jw}=0 or @math{@code{exp}(jwT)}=1) and select the frequency
## range based on the breakpoint locations of the frequencies.
## @item if @var{sys} is discrete time, the frequency range is limited
##               to @math{jwT} in
## @ifinfo
## [0,2 pi /T]
## @end ifinfo
## @iftex
## @tex
## $[0,2\pi/T]$
## @end tex
## @end iftex
## @item A "smoothing" routine is used to ensure that the plot phase does
## not change excessively from point to point and that singular
## points (e.g., crossovers from +/- 180) are accurately shown.
##
## @end enumerate
## @item out_idx
## @itemx in_idx
##
## The names or indices of outputs and inputs to be used in the frequency
## response.  See @code{sysprune}.
##
## @strong{Example}
## @example
## bode(sys,[],"y_3", @{"u_1","u_4"@});
## @end example
## @end table
## @strong{Outputs}
## @table @var
## @item mag
## @itemx phase
## the magnitude and phase of the frequency response @math{G(jw)} or
## @math{G(@code{exp}(jwT))} at the selected frequency values.
## @item w
## the vector of frequency values used
## @end table
##
## @enumerate
## @item If no output arguments are given, e.g.,
## @example
## bode(sys);
## @end example
## bode plots the results to the screen.  Descriptive labels are
## automatically placed.
##
## Failure to include a concluding semicolon will yield some garbage
## being printed to the screen (@code{ans = []}).
##
## @item If the requested plot is for an @acronym{MIMO} system, mag is set to
## @math{||G(jw)||} or @math{||G(@code{exp}(jwT))||}
## and phase information is not computed.
## @end enumerate
## @end deftypefn

## Author: John Ingram <ingraje@eng.auburn.edu>
## Created: July 10, 1996
## Based on previous code by R. Bruce Tenison, July 13, 1994
## Modified by David Clem November 13, 1994
## again by A. S. Hodel July 1995 (smart plot range, etc.)
## Modified by Kai P. Mueller September 28, 1997 (multiplot mode)

function [mag_r, phase_r, w_r] = bode (sys, w, outputs, inputs, plot_style)

  ## check number of input arguments given
  if (nargin < 1 | nargin > 5)
    usage("[mag,phase,w] = bode(sys[,w,outputs,inputs,plot_style])");
  endif
  if(nargin < 2)
    w = [];
  endif
  if(nargin < 3)
    outputs = [];
  endif
  if(nargin < 4)
    inputs = [];
  endif
  if(nargin < 5)
    plot_style = "dB";
  endif

  if (strcmp (plot_style, "dB"))
    do_db_plot = 1;
  elseif (strcmp (plot_style, "mag"))
    do_db_plot = 0;
  else
    error ("bode: invalid value of plot_style specified");
  endif

  [f, w, sys] = __bodquist__ (sys, w, outputs, inputs, "bode");
  bode_nin = sysdimensions(sys,"in");
  bode_nout = sysdimensions(sys,"out");

  [stname,inname,outname] = sysgetsignals(sys);
  systsam = sysgettsam(sys);

  ## Get the magnitude and phase of f.
  mag = abs(f);
  phase = arg(f)*180.0/pi;

  if (nargout < 1),
    ## Plot the information
    save_automatic_replot = automatic_replot;
    unwind_protect
      automatic_replot = 0;
      oneplot();
      __gnuplot_set__ autoscale;
      __gnuplot_set__ nokey;
      clearplot();
      __gnuplot_set__ data style lines;
      if(is_digital(sys))
	xlstr = ["Digital frequency w=rad/sec.  pi/T=",num2str(pi/systsam)];
	tistr = "(exp(jwT)) ";
      else
	xlstr = "Frequency in rad/sec";
	tistr = "(jw)";
      endif
      xlabel(xlstr);
      if(is_siso(sys))
	subplot(2,1,1);
	title(["|[Y/U]",tistr,"|, u=", inname{1},", y=",outname{1}]);
      else
	title([ "||Y(", tistr, ")/U(", tistr, ")||"]);
	disp("MIMO plot from")
	disp(__outlist__(inname,"     "));
	disp("to")
	disp(__outlist__(outname,"    "));
      endif
      wv = [min(w), max(w)];
      if(do_db_plot && max(mag) > 0)
	ylabel("Gain in dB");
	md = 20*log10(mag);
	axvec = axis2dlim([vec(w),vec(md)]);
	axvec(1:2) = wv;
	axis(axvec);
      else
	ylabel("Gain |Y/U|")
	md = mag;
      endif

      grid("on");
      if (do_db_plot)
	semilogx(w,md);
      else
	loglog(w,md);
      endif
      if (is_siso(sys))
	subplot(2,1,2);
	axvec = axis2dlim([vec(w),vec(phase)]);
	axvec(1:2) = wv;
	axis(axvec);
	xlabel(xlstr);
	ylabel("Phase in deg");
	title([ "phase([Y/U]", tistr, ...
	   "), u=", inname{1},", y=",outname{1}]);
	grid("on");
	semilogx(w,phase);
	## This should be the default for subsequent plot commands.
	oneplot();
      endif
    unwind_protect_cleanup
      automatic_replot = save_automatic_replot;
    end_unwind_protect
  else
    mag_r = mag;
    phase_r = phase;
    w_r = w;
  endif
endfunction