Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / control-2.3.52 / nyquist.m

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+## Copyright (C) 2009, 2010, 2012   Lukas F. Reichlin
+##
+## This file is part of LTI Syncope.
+##
+## LTI Syncope 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.
+##
+## LTI Syncope 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 LTI Syncope.  If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{re}, @var{im}, @var{w}] =} nyquist (@var{sys})
+## @deftypefnx {Function File} {[@var{re}, @var{im}, @var{w}] =} nyquist (@var{sys}, @var{w})
+## Nyquist diagram of frequency response.  If no output arguments are given,
+## the response is printed on the screen.
+##
+## @strong{Inputs}
+## @table @var
+## @item sys
+## LTI system.  Must be a single-input and single-output (SISO) system.
+## @item w
+## Optional vector of frequency values.  If @var{w} is not specified,
+## it is calculated by the zeros and poles of the system.
+## Alternatively, the cell @code{@{wmin, wmax@}} specifies a frequency range,
+## where @var{wmin} and @var{wmax} denote minimum and maximum frequencies
+## in rad/s.
+## @end table
+##
+## @strong{Outputs}
+## @table @var
+## @item re
+## Vector of real parts.  Has length of frequency vector @var{w}.
+## @item im
+## Vector of imaginary parts.  Has length of frequency vector @var{w}.
+## @item w
+## Vector of frequency values used.
+## @end table
+##
+## @seealso{bode, nichols, sigma}
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: November 2009
+## Version: 0.3
+
+function [re_r, im_r, w_r] = nyquist (sys, w = [])
+
+  ## TODO: multiplot feature:   nyquist (sys1, "b", sys2, "r", ...)
+
+  if (nargin == 0 || nargin > 2)
+    print_usage ();
+  endif
+
+  [H, w] = __frequency_response__ (sys, w, false, 0, "ext");
+
+  H = reshape (H, [], 1);
+  re = real (H);
+  im = imag (H);
+
+  if (! nargout)
+    plot (re, im, "b", re, -im, "r")
+    axis ("tight")
+    xlim (__axis_margin__ (xlim))
+    ylim (__axis_margin__ (ylim))
+    grid ("on")
+    title (["Nyquist Diagram of ", inputname(1)])
+    xlabel ("Real Axis")
+    ylabel ("Imaginary Axis")
+  else
+    re_r = re;
+    im_r = im;
+    w_r = w;
+  endif
+
+endfunction
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