Calculate the value of a symbolic experession

[Leo Baumann]

Hello,

I am newbie to Octave and have the problem to calculate the value for a 
symbolic expression for an argument. -

>> ux
ux = (sym)

                   /      75*pi  \                    / 25*pi  \
  Heaviside|t - ---------|   Heaviside|t - ---------|
                   \    310895263/            \    310895263/
                  ------------------------ + ------------------------
                                     6                          2

>> td
td =   2.5262e-007
>> t=2*td
t =   5.0525e-007
>>

I don't find the syntax for calculation of ux(t) in the help files. I 
want to calculate ux at the point t.

Anyone can help me, please?

Regards - Leo