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## Bode plot with asymptotes

version 1.2.0.0 (3.4 KB) by Trond Andresen

### Trond Andresen (view profile)

Bode plot with asymptotes

Updated 16 Feb 2017

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

### Cite As

Trond Andresen (2020). Bode plot with asymptotes (https://www.mathworks.com/matlabcentral/fileexchange/10183-bode-plot-with-asymptotes), MATLAB Central File Exchange. Retrieved .

Nate Castle

### Nate Castle (view profile)

Works well. Only issue I encountered was that it wasn't displaying correctly when I had it within a subplot.

Esteban Acevedo Rivillas

andy Chang

Thomas Pandolfi

Jon Walderhaug

Trond Andresen

### Trond Andresen (view profile)

Sorry, saw your correction just now. But the same holds there, asymp(.) and bode(.) both gives amp = 0dB for freq = 1 rad/s.

Fausto Orozco Coy

### Fausto Orozco Coy (view profile)

Excuse me I mean 1 rad/s must have 0 dB gain

Fausto Orozco Coy

### Fausto Orozco Coy (view profile)

This is the transfer function I'm testing:

num=-999.9000e-003;
den=[9.9990e-009 1.0000e+000 0.0000e+000];
H=tf(num,den);
asymp(H,2*pi*1e-3,62.8319e+009);

this is a video showing when I maximize the figure, the xaxis tick labels don't correspond to the right values (0 rad/s must have 0 dB gain)

https://youtu.be/1Dm0kcWD6pQ

Trond Andresen

### Trond Andresen (view profile)

I am the author of this program. Can you Fausto, tell which transfer function you used that resulted in wrong x-axis tick labels? Then I will check it myself.

Fausto Orozco Coy

### Fausto Orozco Coy (view profile)

awesome function, very useful in the learning of bode diagrams, thanks a lot, however in MatLab 2017 live editor when a figure is open in a figure window the x axis ticks labels don't correspond to the real position.

Alessandro Ballio

Awesome!

Stone Shek

### Stone Shek (view profile)

Matteo Luciardello Lecardi

Josep Guasch

Josep Guasch

### Josep Guasch (view profile)

David Gonzalez Bravo

### David Gonzalez Bravo (view profile)

Very useful!!!

It works perfect, Thanks.

Trond Andresen

### Trond Andresen (view profile)

Re error msg from Chantal Muller:
If h(s) = num(s)/den(s), the transfer function has to have degree(num) <= degree(den), i.e. be proper or strictly proper.

Robert Stengel

### Robert Stengel (view profile)

Suggested improvement: Add gridlines. Find all calls to MATLAB's 'bode.m', and add ', grid'.

Robert Stengel

### Robert Stengel (view profile)

Auto-completion error: 'asymptotic.m' should be 'asymp.m'.

Chantal MULLER

### Chantal MULLER (view profile)

Great !
But I don't understand why the function fails to plot:
H1=1+s/10
H2=1-s/10
wheareas there s no pb with :
H7=(10*s^2+5*s+10)/(1+s/10)
I was thinking there was a constrain d°(den)< d°(num), but H7 works.

Nico Sjursen

Ed Sar

### Ed Sar (view profile)

Britany Chamberlain

Ostheer

### Ostheer (view profile)

good work, thanks

Trond Andresen

### Trond Andresen (view profile)

I am the author of this function. It works also for the counter-examples given here by other commenters.

Aim Dulay

Rafael Crepaldi

Marcos Gonzalez

Yngve

### Yngve (view profile)

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

Robert Stengel

### Robert Stengel (view profile)

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)

Moussab Bennehar

Moussab Bennehar

### Moussab Bennehar (view profile)

You're a Geeeeeeeeeeenius
really, great m file
thanx

Robert

### Robert (view profile)

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

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

John babs

great stuff. thanks!

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);
----------------

Trung Duong

It's work. Nice job

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.

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);

Zain Gurraya

Jiro Doke

A similar submission:

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.