How to plot step response of second order system?

omgNot = 1;
zetaNot = 0.6;
H = tf(omgNot^2,[1, 2*zetaNot*omgNot, omgNot^2]);
stepplot(H)

I am using the code above to plot the step response of a second order system, but I am getting the follwoing error

Invalid default value for property 'InputName_' in class

'DynamicSystem':

Attempt to execute SCRIPT strings as a function:

I would really appreciate your help. Thank you.

[madhan ravi]

Upload the script file that you are executing.

[theblueeyeswhitedragon]

The code above is all I have in the script

[madhan ravi]

Might happen you have a script file named as a function. What shows up? when you type the below in command window post the results:

which tf -all 
which stepplot -all

[theblueeyeswhitedragon]

>> which tf -all 
which stepplot -all
C:\Program Files\MATLAB\R2017b\toolbox\control\ctrlmodels\@tf\tf.m                 % tf constructor
C:\Program Files\MATLAB\R2017b\toolbox\control\ctrlmodels\@DynamicSystem\tf.m      % DynamicSystem method
C:\Program Files\MATLAB\R2017b\toolbox\dsp\filterdesign\@mfilt\tf.m                % mfilt method
C:\Program Files\MATLAB\R2017b\toolbox\shared\controllib\engine\@StaticModel\tf.m  % StaticModel method
C:\Program Files\MATLAB\R2017b\toolbox\signal\signal\@dfilt\tf.m                   % dfilt method
C:\Program Files\MATLAB\R2017b\toolbox\shared\controllib\engine\@DynamicSystem\stepplot.m  % DynamicSystem method

[madhan ravi]

Not certain where exactly the problem lies but you seem to be missing:

/Applications/MATLAB_R2018b.app/toolbox/ident/ident/@idParametric/tf.m              % idParametric method

[theblueeyeswhitedragon]

How do i fix this problem? Is there a way to add the .m file to this folder?

[madhan ravi]

The best option is to contact mathworks support team by clicking the Contact Us button on the top right corner if this page. And finally post the solution (the reason) provided by them as an answer and accept it so it might be helpful for others.

Answer 1

[Hiroumi Mita]

Do you have any MATLAB workspace variables pre-defined and the name is such as,'tf' ,'sterpplot', or ' DynamicSystem'?

Needless to say, double defined same name of pre-defined functions and workspace variable is prohibited.

The reason is priority of workscape name and functionname depends on the prioirty of MATLAB path.

If you have 'tf' where is in MATLAB workspace variable , this is the highest priority.

Second, if you have 'tf' function or other famous name's function you personally programed in current directory which name is same as functions as provided by toolboxes , the function located in current directory has higher priority than Toolboxes.

Please check above.

In my environment , your scriput runs normally.

[madhan ravi]

It would have been crystal clear when typing

which ... -all

as the OP has posted the results of it , neither it is a variable or a custom made function/script. Possible reason could be that the OP has made some changes in the default script file.

Answer 2

[Vikas Panit]

You can use the MATLAB pre-defined variables of Control Systems Toolbox to solve the following problem. If you dont have Control Systems toolbox download from here - https://in.mathworks.com/products/control.html

Here is the code you can use to find step response of second order system and command window output:

wn= input('frequency')
zeta= input('damping factor')
k= input('constant')
num= [k*wn^2]
deno= [1 2*zeta*wn wn^2]
g= tf(num, deno)
t= feedback(g,1)
step(t, 'r')

Answer 3

[Martial Mezatio]

clear all

close all

s=tf(s);

g=1/2*s+1);

step_g/s)

Answer 4

[Afshan.N.]

wn= input('frequency') zeta= input('damping factor') k= input('constant') num= [k*wn^2] deno= [1 2*zeta*wn wn^2] g= tf(num, deno) t= feedback(g,1) step(t, 'r')