Re: A question regarding unwrap

[Doug Stewart]

Ron Crummett wrote:

> Hi -
>
> I have a recent problem with unwrap; I tried plotting the phase of a 
> transfer function and it jumped halfway through the plot, from -180 to 
> 180.  I tried to unwrap the phase using unwrap and plotted the phase 
> again, but still had the same jump.  Reading the help on unwrap, it 
> sounds like it will only really work if the phase is positive (it adds 
> 2*pi).  For me, I have a negative phase, so I need to subtract 2*pi.  
> Any idea of what the solution could be?  I tried looking at the code 
> but couldn't make too much sense out of it from my few glances.
>
> Thanks,
>
> Ron Crummett
This is not about unwrap bur it might do what you want  and more  :-)
Let me know if you want more help.
Doug


## Copyright (C) 2004 doug
##
## 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     bode1 (n,d)
%n= numerator
% d=denominator
%

## bode1w

## Author: doug
##
## 2004-09-27 doug
## * Initial revision
## Rev #1  Nov 29 2004 Doug Stewart

function     bode1w (n,d);

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

# fix the phase wrap arownd
ll=length(ph);
[qm iqm]=max(abs(diff(ph)));
if(qm>300)
ph(iqm+1:ll)=ph(iqm+1:ll)-360;
endif


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







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