hey so i need to repeat the code everytime to see and analyze the time responses for 20 different values of k. How can i do it at once and have the output for all the values?

% Time response problme #3
% time response and pole zero plot
k=input('Enter the value of k');
ng1=[k];dg1=[1];
ng=[20]; dg=[1 1 5];
[na, da]=series(ng,dg,ng1,dg1)
[num, den]=cloop(na,da)
sys=tf(num,den)
[z,p,k]=tf2zp(num,den)
subplot(1,2,1);step(sys,20e-1)
S = stepinfo(sys)
subplot(1,2,2); zplane(num,den)

[Sam Chak]

Hi @Pragna

The 'cloop()' function has been outdated for over two decades. It seems like you may have copied the code from very old books, or your professor provided you with legacy code for completing the homework questions. Additionally, 'zplane' is used to create a zero-pole plot for discrete-time systems, but your systems are continuous-time.

help cloop

    CLOOP is obsolete, use FEEDBACK instead.

Have you considered replacing the 'cloop()' function with the 'feedback()' function in the code? This change could help simplify the problem by allowing you to create a single plot for a scalar value of the gain k.

By doing so, you can evaluate if the plot is correctly displayed as desired. If this approach proves successful, you can then tackle the problem using the for-loop approach and the supplied values of 'k'.

[Pragna]

hhey thanks ....they did teach us bout both cloop and feedback in class but what did you mean by zplane being used only for discrete time systems ??? is there any other functions wrt to continuous time systems???

Answer 1

[Infinite_king]

Hi Pragna,

You can use 'for' loop to execute the same code on different values.

% Store all input values in an array
input_values = [ 1 2 3 ];

% execute the code in a for loop
for single_input_value = input_values % loop will execute
    k = single_input_value;
    % place the remaining code inside the for loop
    ng1=[k];dg1=[1];
    ng=[20]; dg=[1 1 5];
    [na, da]=series(ng,dg,ng1,dg1)
    [num, den]=cloop(na,da)
    sys=tf(num,den)
    [z,p,k]=tf2zp(num,den)
    % create new figure for each iteration
    figure();
    subplot(1,2,1);step(sys,20e-1)
    S = stepinfo(sys)
    subplot(1,2,2); zplane(num,den)
end

na = 1x3

0 0 20

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da = 1x3

1 1 5

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num = 1x3

0 0 20

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den = 1x3

1 1 25

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sys =
 
       20
  ------------
  s^2 + s + 25
 
Continuous-time transfer function.

z =

  0x1 empty double column vector

p = 
  -0.5000 + 4.9749i
  -0.5000 - 4.9749i

k = 20

S = struct with fields:
         RiseTime: 0.2254
    TransientTime: 7.6746
     SettlingTime: 7.6746
      SettlingMin: 0.3748
      SettlingMax: 1.3833
        Overshoot: 72.9156
       Undershoot: 0
             Peak: 1.3833
         PeakTime: 0.6283

na = 1x3

0 0 40

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<mw-icon class=""></mw-icon>

da = 1x3

1 1 5

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<mw-icon class=""></mw-icon>

num = 1x3

0 0 40

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den = 1x3

1 1 45

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sys =
 
       40
  ------------
  s^2 + s + 45
 
Continuous-time transfer function.

z =

  0x1 empty double column vector

p = 
  -0.5000 + 6.6895i
  -0.5000 - 6.6895i

k = 40

S = struct with fields:
         RiseTime: 0.1646
    TransientTime: 7.5945
     SettlingTime: 7.5945
      SettlingMin: 0.3332
      SettlingMax: 1.5917
        Overshoot: 79.0688
       Undershoot: 0
             Peak: 1.5917
         PeakTime: 0.4683

na = 1x3

0 0 60

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<mw-icon class=""></mw-icon>

da = 1x3

1 1 5

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<mw-icon class=""></mw-icon>

num = 1x3

0 0 60

<mw-icon class=""></mw-icon>

<mw-icon class=""></mw-icon>

den = 1x3

1 1 65

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<mw-icon class=""></mw-icon>

sys =
 
       60
  ------------
  s^2 + s + 65
 
Continuous-time transfer function.

z =

  0x1 empty double column vector

p = 
  -0.5000 + 8.0467i
  -0.5000 - 8.0467i

k = 60

S = struct with fields:
         RiseTime: 0.1356
    TransientTime: 7.7949
     SettlingTime: 7.7949
      SettlingMin: 0.2984
      SettlingMax: 1.6824
        Overshoot: 82.2648
       Undershoot: 0
             Peak: 1.6824
         PeakTime: 0.3897

Refer the following documentation to know more about 'for' loops - https://www.mathworks.com/help/matlab/ref/for.html

[Pragna]

Thank youu :)

Answer 2

[Paul]

Or use a model array

plant = tf(20,[1 1 5]);
k     = realp('k',1);
sys   = feedback(k*plant,1);
sysarr = sampleBlock(sys,'k',linspace(1,20,5));
figure
stepplot(sysarr)

If rather put each plot on a separate axis, then

N = nmodels(sysarr);
figure
h = cellfun(@(sys) stepplot(axes(figure),sys),squeeze(mat2cell(sysarr,1,1,ones(1,N),1)));

[Sam Chak]

👍

Answer 3

[Anton Kogios]

There are many ways to go about this and your question is not very specific in what you want. What values do you want to keep?

One way is to use a for loop:

k=1:20; % enter your 20 values of k

for i = 1:length(k)
    ng1=[k(i)];dg1=[1];
    ng=[20]; dg=[1 1 5];
    [na, da]=series(ng,dg,ng1,dg1)
    [num, den]=cloop(na,da)
    sys=tf(num,den)
    [z,p,k]=tf2zp(num,den)
    figure(i)
    subplot(1,2,1);step(sys,20e-1)
    S = stepinfo(sys)
    subplot(1,2,2); zplane(num,den)
end

Note that k will get overwritten by the output of tf2zp, so name it something else if you want to keep it.

[Pragna]

hey thanks but it shows an error.....

[Sam Chak]

Hi @Pragna, actually, if you read @Anton Kogios' earlier explanations, he clarified that using the same 'k' variable in the output argument of the 'tf2zp' function will overwrite it. Changing that, as he suggested, should fix the issue.

Remember, it's important not to blindly copy and paste the code. Take the time to understand what each line does if you want to learn. Also, please keep in mind that just because @Infinite_king's code works, it doesn't necessarily mean it follows good programming practices, especially when dealing with for-loops.

% Store all input values in an array

input_values = [1 2 3];

% execute the code in a for loop

for single_input_value = input_values % loop will execute

...

end

Modification on @Anton Kogios's code:

k = 1:4.75:20;

for i = 1:length(k)
    G1          = tf(k(i));
    G2          = tf(20, [1 1 5]);
    Gcl         = feedback(G1*G2, 1);   % closed-loop TF
    [z, p, K]   = zpkdata(Gcl, 'v');    % <-- do not use the same 'k'
    figure(i)
    subplot(1,2,1); 
    step(Gcl), grid on
    S = stepinfo(Gcl);
    subplot(1,2,2); 
    rlocus(Gcl), grid on
end