Hi. I have problems with transfer function and Laplace

Hi everyone. I'm new with Matlab. I have 2 problems:

1. if i run this code

syms s
numh=[1 1]
denh=[1 2 1]
H=tf(numh,denh)
h=ilaplace(H)

i have this error: Check for missing argument or incorrect argument data type in call to function 'ilaplace'.

2. instead if i run this code

syms s
numh=[1 1]
denh=[1 2 1]
H=tf(numh,denh)
h=ilaplace((s+1)/(s^2+2s+1))

i have this error: Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.

Answer 1

[Star Strider]

Control System Toolbox objects and Symbolic Math Toolbox objects are inherently incompatible. It takes a bit of effort to get them to talk to each other, and is occasionally worth the effort.

I would just do this:

syms s t 
h=ilaplace((s+1)/(s^2+2*s+1))

producing:

h =
exp(-t)

If you want the Bode plot or impulse function of the system from the Control System Toolbox, use:

numh=[1 1]
denh=[1 2 1]
H=tf(numh,denh)

and the the appropriate functions.

Answer 2

[Ameer Hamza]

Symbolic toolbox and control system toolbox are not compatible. You cannot input a transfer function to ilaplace, therefore the first code does not work. Following shows the issue in 2nd code

syms s
numh=[1 1]
denh=[1 2 1]
h=ilaplace((s+1)/(s^2+2*s+1))
                      %^ put * here