Why do I receive an error when I run this code?

Why do I receive an error when I run this code?

   sys=tf([1],[1 1],'InputDelay',2)  
        sysd=c2d(sys,0.5)
       [num,den]=tfdata(sysd)
        num=num2str(num{:})
        den=num2str(den{:})
        num=poly2sym(num,z)
        den=poly2sym(den,z)
        num=char(num)
        den=char(den)

Answer 1

[Paulo Silva]

Bad use of the poly2sym function, you give a string for the first argument but the function expects one array.

Also the z should be like this 'z'

doc poly2sym

Just a tip: num{:} gives you one array, that array can be used by poly2sym

sys=tf([1],[1 1],'InputDelay',2)
sysd=c2d(sys,0.5)
[num,den]=tfdata(sysd)
num=vpa(poly2sym(num{:},'z'),4)
den=vpa(poly2sym(den{:},'z'),4)
nums=char(num)
dens=char(den)

There were some errors, I had to edit the answer several times but I think that now it's all working.

[sadel]

I removed the num2str function and I receive a very big result

num =

1772028374299899/4503599627370496

den =

z - 2731571253070597/4503599627370496

Why?

[Paulo Silva]

Because it's the exact value.

[Paulo Silva]

you can see the same behavior in the documentation example

doc poly2sym

[Paulo Silva]

ok I fixed the code again, no more big and precise values, happy now?

[sadel]

hahaha yes, thank you very much!!!!

Answer 2

[Julián Francisco]

My Matlab program says that you have not defined the variable z.

[Paulo Silva]

it should be like this 'z' instead of just z