## Copyright (C) 2004 Doug Stewart
## 
## 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

% 
%function     bode1w (n,d)
%n= numerator
%d=denominator
%
% This was written to help my students with Gain Margin and Phase Margin
%GM and PM lines are added to the Bode plot and 
%GM and PM values are printed on the screen.


## bode1w

## Author: doug 
## 
## 2004-09-27 doug 
## * Initial revision
## Rev #1  Nov 29 2004 Doug Stewart
## Rev #2 Sept 2005 Doug Stewart 
##              - Added the If for negative phase steps.
##              - and the DO loop
## Rev #3 Sept 2005 Doug Stewart
##              - used unwrap.m

function     bode1w (n,d);

sys=tf2sys(n,d);
[mag,ph,w]=bode(sys);


# fix the phase wrap arownd
phw=unwrap(ph*pi/180);
ph=phw*180/pi;
%do
	ll=length(ph);
%	[qm iqm]=max((diff(ph)));
%	if(qm>300)
%	 ph(iqm+1:ll)=ph(iqm+1:ll)-360;
%	endif
%	[qm iqm]=min((diff(ph)));
%	if(qm<-300)
%	ph(iqm+1:ll)=ph(iqm+1:ll)+360;
%	endif
%until (abs(qm)<300)




# make a 180 deg line
v=ones(ll,1)*(-180);
db=20*log10(mag);

# find the Gain Margin  and its location
[x ix]=min(abs(ph+180));
if (x>1)
GM="INF"
ix=length(ph);
else
Gm=20*log10(mag(ix))
endif

# find the Phase Margin and its location
[pmx ipmx]=min(abs(mag-1));
PM=180+ph(ipmx)


#f=w/(2*pi);
semilogx(w,db,1,0,w,ph,w,v,[w(ix) w(ix)],[30 -180] ,[w(ipmx) w(ipmx)],[0 -200])
#gset grid mxtics xtics ytics
#replot
 
endfunction