Bode

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Diego Aguilera
Diego Aguilera 2011-7-6
评论： Hamed Pouria 2019-7-6
I am new to Matlab. I need to use the Bode command. When I run my code, I get this error: "Undefined function or method 'bode' for input arguments of type 'double'."

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回答（3 个）

Oleg Komarov
Oleg Komarov 2011-7-6
You may not have the Control System Toolbox. To check that type ver in the command window.
Paulo Silva
Paulo Silva 2011-7-6
Besides Oleg suggestion, bode doesn't take double arguments, you must provide one transfer function instead.
%simple example from the bode function documentation
g = tf([1 0.1 7.5],[1 0.12 9 0 0]);
bode(g)
Reference: bode function
Here's a way to do the bode plot without the control toolbox:
sys=@(s) (s.^2+0.1*s+7.5)./(s.^4+0.12.*s.^3+9*s.^2)
w=1:0.01:40;
amp=10*log10(abs(sys(w*i)));
ang=angle(sys(w*i))*180/pi;
subplot(211)
plot(w,amp)
title(char(sys))
ylabel('Magnitude (DB)')
set(gca,'xscale','log')
subplot(212)
plot(w,ang)
set(gca,'xscale','log')
xlabel('frequency (rad/sec)')
ylabel('phase (deg)')
  2 个评论
Seng Tak Goh
Seng Tak Goh 2019-4-18
Hi Paulo,
That was amazing! Do you mind to explain how sys=@(s) actually does the trick?
Many thanks in advance!
Hamed Pouria
Hamed Pouria 2019-7-6
It has some promlems.
in line 3 you must write :
amp=20*log10(abs(sys(w*i)));
and also if the number of poles - number of zeros of the system will be bigger than 2 (for example 3) it does not work correctly because of the strict of the function angle(); It will return the phase angles only within the interval [-pi to pi].

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Diego Aguilera
Diego Aguilera 2011-7-6
I'm guessing it's not installed...
-------------------------------------------------------------------------------------
MATLAB Version 7.11.0.584 (R2010b)
MATLAB License Number: ###########[SCd Censor]
Operating System: Mac OS X Version: 10.6.7 Build: 10J869
Java VM Version: Java 1.6.0_24-b07-334-10M3326 with Apple Inc. Java HotSpot(TM) 64-Bit Server VM mixed mode
-------------------------------------------------------------------------------------
MATLAB Version 7.11 (R2010b)
Simulink Version 7.6 (R2010b)
Curve Fitting Toolbox Version 3.0 (R2010b)
SimPowerSystems Version 5.3 (R2010b)
  2 个评论
Oleg Komarov
Oleg Komarov 2011-7-6
No guess here.
Diego Aguilera
Diego Aguilera 2011-7-6
Ha. I'm upgrading to the newest version. I believe the it has the Control System Toolbox. I'll find out in a few hours. Thanks.

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