CODEWITHSUNDEEP
matlab
alim1990
alim1990

Reputation: 4972

Plotting a transfer function in a range of values giving error of plot Not enough input arguments

I need to see at which values of kc a system is stable and unstable.

The system has the following transfer function:

(-2Kc)/(s^4+3s^3+4s^2+3s+(1-2kc) )

enter image description here

After calculations, for this system to be stable, kc should be in this range of values:

-1 < Kc < 0.5

I am using matlab, and added the following to plot the transfer function response for each value of Kc from -2 to 1 with a step of 0.1:

syms s kc;

t=(-2*kc)/(s^4+3*s^3+4*s^2+3*s+1-2*kc);

kc=-2:0.1:1;

plot(t)

I got the following errors:

Error using plot Data must be numeric, datetime, duration or an array convertible to double.

Error using plot. Not enough input arguments.

I tried to step function but got the same error.

Upvotes: 0

Views: 1842

Answers (1)

AVK
AVK

Reputation: 2149

The error message says that t is not a numeric array. t is a symbolic object; the plot function knows nothing about symbolic objects and can't handle them properly. The second issue is that the kc variable definition

kc=-2:0.1:1;

has no effect because it does not affect the content of the symbolic object t.

There is a function ezplot, which plots symbolic objects. Also, you need a loop:

syms s 

for kc=-2:0.1:1;
    t=(-2*kc)/(s^4+3*s^3+4*s^2+3*s+1-2*kc);
    ezplot(t);
    hold on;
end

In order to plot the step response, you can use the Control System Toolbox:

for kc=-2:0.25:1;
    h = tf(-2*kc,[1 3 4 3 1-2*kc]);
    step(h,10);
    hold on;
end

Upvotes: 1

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