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Bode plot with asymptotes

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28 Feb 2006 (Updated )

Bode plot with asymptotes

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Description

The function asymp() corresponds to bode(), but it also plots asymptotes for the magnitude and phase graphs. Phase asymptotes are vertical.

asymp() only accepts monovariable transfer functions.

If the transfer function also has a time delay, the time delay is ignored
for the phase asymptotes.

asymp() may be called in two ways only, asymp(h), or asymp(h,wmin,wmax).

Required Products Control System Toolbox
MATLAB release MATLAB 7.6 (R2008a)
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Comments and Ratings (14)
23 Jun 2012 Marcos Gonzalez  
24 Apr 2012 Yngve

The asymptotes does not work for angles in this bandstop-filter:

>> H = tf([1 0 4000.*16000],[1 4000+16000 4000.*16000])

Transfer function:
s^2 + 6.4e007
-----------------------
s^2 + 20000 s + 6.4e007

>> asymp (H)

(Maybe because of the sudden 180 degree phase shift at the bandstop frequency)

Other than that, the program is wonderful <3

06 Jan 2011 Robert Stengel

It doesn't work with this simple test:
f11 = -1.2794;
f12 = -7.9856;
f22 = -1.2709;
F = [f11 f12;1 f22];
G = [-f12;0];
Hx = [1 0];
B22 = inv(-Hx*inv(F)*G)
sys = ss(F, G*B22, Hx,0);
figure
step(sys), grid
figure
bode(sys),grid
figure
asymp(sys)

12 Mar 2010 Bennehar Moussâb  
12 Mar 2010 Bennehar Moussâb

You're a Geeeeeeeeeeenius
really, great m file
thanx

17 Oct 2009 Robert

i need help...it keeps saying error at asymp at 19

12 May 2008 Nabil al-hadawy

******* Thank you **********
This is function (asymp.m) very nice

09 Apr 2008 John babs

great stuff. thanks!

04 Dec 2007 Joseph Birbiglia

Very good, but there are errors with the following transfer function:

G(s) = (s^2+1)/(s*(s^2+4))

---------
??? Error using ==> colon
Maximum variable size allowed by the program is exceeded.

Error in ==> asymp at 147
set(get(gcf, 'CurrentAxes'),'YTick',magmin:ydelta:magmax);
----------------

12 Nov 2007 Trung Duong

It's work. Nice job

04 Apr 2007 Trond Andresen

I am the author of asymp( ).The problem reported by Anton Cervin has now been fixed. Please tell me if problems still remain.

29 Sep 2006 Anton Cervin

It does not seem to work.

>> G = (s+1)/(s*(s+10))

Transfer function:
s + 1
----------
s^2 + 10 s

>> asymp(G)
??? Error using ==> axes
Invalid object handle.

Error in ==> asymp at 120
axes(h);

18 Jun 2006 Zain Gurraya  
02 Mar 2006 Jiro Doke

A similar submission:

http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=2664&objectType=file

I would appreciate a more comprehensive help text at the top. The code is documented pretty well. There are some coding styles that could be better (i.e. the while loops). Since you are plotting the asymptotes, maybe the function could return the break frequencies and the corresponding slopes of the asymptotes. It can have the same behavior as BODE, in which if there are no output arugments, then it would create a plot, and if there are outputs, then it wouldn't create a plot.

Updates
16 Mar 2007

Fix error: A reviewer pointed out that a certain transfer function didn't work with the current version.

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