Error when using step-command

I want to plot the step response of a transfer function but when I use step() i get an error message. I have tried to paste example-code from the matlab help but I still get error.

This is the example code:

(https://se.mathworks.com/help/control/ref/lti.step.html#d122e120846)

sys = tf(4,[1 2 10]);

step(sys)

The message I get is:

"Unable to use a value of type tf as an index."

Anyone who knows what might be wrong?

[Jon]

I can't reproduce the problem running R2020a Update 3. I get a nice step response plot with those same two commands.

I assume you have tried clearing the workspace first, or reopening MATLAB completely just to make sure that there isn't some other variable assignment confusing things, and then, just type those two lines of code

Answer 1

[Star Strider]

I strongly suspect that you have a variable named ‘step’.

Run this is a script or your Command Window:

which step -all

I suspect the first line will be:

step is a variable.  

If so, rename the variable to something else that is relevant to the context.

[Fangjun Jiang]

make sense

>> step=1:12
step =
     1     2     3     4     5     6     7     8     9    10    11    12
>> step(sys)
Unable to use a value of type tf as an index.

[Marcus Carlsson]

Hi!

You were right, thank you very much!

[Star Strider]

As always, my pleasure!

Answer 2

[Fangjun Jiang]

tf() is supposed to define a Transfer Function. You might have a variable called "tf" or other function called "tf". Do the following and see what are the returns

tf
which -all tf