## Copyright (C) 1996, 1998 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.
##
## 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, write to the Free
## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 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 @var{T}=@code{sysgettsam(@var{sys})} (the system sampling time) and
## @item @math{G(z)} is the system transfer function.
## @end itemize
##
## @strong{ Default} the default frequency range is selected as follows: (These
## steps are 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 indices of the output(s) and input(s) to be used in
## the frequency response; see @code{sysprune}.
## @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
##
## @strong{Notes}
## @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 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] = __bodquist__ (sys, w, outputs, inputs, "bode");

  [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
    if(gnuplot_has_multiplot)
      oneplot();
    endif
    gset autoscale;
    if(gnuplot_has_multiplot)
      gset nokey;
    endif
    clearplot();
    gset 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))
      if (gnuplot_has_multiplot)
        subplot(2,1,1);
      endif
      title(["|[Y/U]",tistr,"|, u=", nth(inname,1),", y=",nth(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))
      if (gnuplot_has_multiplot)
        subplot(2,1,2);
      else
        prompt("Press any key for phase plot");
      endif
      axvec = axis2dlim([vec(w),vec(phase)]);
      axvec(1:2) = wv;
      axis(axvec);
      xlabel(xlstr);
      ylabel("Phase in deg");
      title([ "phase([Y/U]", tistr, ...
         "), u=", nth(inname,1),", y=",nth(outname,1)]);
      grid("on");
      semilogx(w,phase);
      ## This should be the default for subsequent plot commands.
      if(gnuplot_has_multiplot)
        oneplot();
      endif
    endif
  else
    mag_r = mag;
    phase_r = phase;
    w_r = w;
  endif
endfunction