Error exploring a Matlab example

[jmb]

Hello,

I am toying with a Matlab for control loop example that I found here:
        
http://www.mathworks.com/help/control/examples/temperature-control-in-a-heat-exchanger.html

The problem is I get:
        Gp = exp(-theta*s)/(1+tau*s)
        error: exp: not defined for class

But alternates like:
octave>>Gp = 1/(1+tau*s)
        Transfer function 'Gp' from input 'u1' to output ...
                  1
        y1:  ----------
              21.3 s + 1
        Continuous-time model.

octave>>Gp = (-theta*s)/(1+tau*s)
        Transfer function 'Gp' from input 'u1' to output ...
               -14.7 s
         y1:  ----------
              21.3 s + 1
        Continuous-time model.
Do work...

It appears that the exp() function is not able to handle a (Laplace
Transform) transfer function variable.  Any ideas, thoughts or help
would be very much appreciated.

Again the relevant version info:
        octave:2> version 3.8.1
        octave:3> pkg list
        Package Name    | Version | Installation directory
        ----------------+---------+-----------------------
                   io *|   2.2.4 | /home/.../octave/io-2.2.4

        lsb_release -a
        Description:    Ubuntu 12.04.5 LTS

        uname -a
        Linux ... 3.5.0-55-generic #82~precise1-Ubuntu SMP x86_64 x86_64 x86_64
GNU/Linux

Regards, JMB