[Octave-cvsupdate] SF.net SVN: octave:[5988] trunk/octave-forge/main/control

[<sla...@us...>]

Revision: 5988
          http://octave.svn.sourceforge.net/octave/?rev=5988&view=rev
Author:   slackydeb
Date:     2009-07-06 09:06:55 +0000 (Mon, 06 Jul 2009)

Log Message:
-----------
Add margin (thanks to Lukas Reichlin <luk...@sw...>).

Modified Paths:
--------------
    trunk/octave-forge/main/control/INDEX

Added Paths:
-----------
    trunk/octave-forge/main/control/inst/margin.m

Modified: trunk/octave-forge/main/control/INDEX
===================================================================
--- trunk/octave-forge/main/control/INDEX	2009-07-06 08:58:15 UTC (rev 5987)
+++ trunk/octave-forge/main/control/INDEX	2009-07-06 09:06:55 UTC (rev 5988)
@@ -55,6 +55,7 @@
  bode bode_bounds nichols
  freqchkw ltifr nyquist tzero tzero2
  rlocus
+ margin
 Controller design
  dgkfdemo hinfdemo dhinfdemo
  dlqe dlqr lqe lqg lqr 

Added: trunk/octave-forge/main/control/inst/margin.m
===================================================================
--- trunk/octave-forge/main/control/inst/margin.m	                        (rev 0)
+++ trunk/octave-forge/main/control/inst/margin.m	2009-07-06 09:06:55 UTC (rev 5988)
@@ -0,0 +1,76 @@
+## Copyright (C) 2009 Doug Stewart and Lukas Reichlin
+## 
+## 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 2 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; if not, write to the Free Software
+## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+## -*- texinfo -*-
+## @deftypefn{Function File} {[@var{gamma}, @var{phi}, @var{w_gamma}, @var{w_phi}] =} margin (@var{sys})
+## Gain and phase margins.
+##
+## @strong{Inputs}
+## @table @var
+## @item sys
+## Continuous time system.
+## @end table
+##
+## @strong{Outputs}
+## @table @var
+## @item gamma
+## Gain margin (as gain, not dbs).
+## @item phi
+## Phase margin (in degrees).
+## @item w_gamma
+## Radian frequency for the gain margin.
+## @item w_phi
+## Radian frequency for the phase margin.
+## @end table
+##
+## @seealso{bode}
+## @end deftypefn
+
+## Version: 0.1alpha
+
+
+function [gamma, phi, w_gamma, w_phi] = margin(sys)
+
+  if (nargin != 1 || (! isstruct (sys)))
+    print_usage ();
+  endif
+
+  ## Get Frequency Response
+  [mag, pha, w] = bode (sys);
+
+  ## fix the phase wrap around
+  phw = unwrap (pha * pi/180);
+  pha = phw * 180/pi;
+
+  ## find the Gain Margin and its location
+  [x, ix] = min (abs (pha + 180));
+
+  if (x > 1)
+    gamma = "INF";
+    ix = length (pha);
+  else
+    gamma = 1 / mag(ix);
+  endif
+
+  w_gamma = w(ix);
+
+  ## find the Phase Margin and its location
+  [pmx, ipmx] = min (abs (mag - 1));
+
+  phi = 180 + pha(ipmx);
+  w_phi = w(ipmx);
+
+endfunction 


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