[Signal] Algebraic representation of thansfer function

[cypselos]

Hello.

I'm using Octave 3.0.1.

There's an exponential in the transfer function I need to use. So I can't use 
tf. I found this code :

s=zpk('s');
h=exp(s);

but it doesn't work with Octave. I also read that zpk should be replaced by 
zp2sys but zp2sys('s') generates an error.

I have also tried

s=tf([1 0], [1]);
h=exp(s);

but it still bugs, whereas it works under Matlab...

Thanks.