Creo Simulate > Additional Information > Working with Functions > Function Definition Dialog Box > Symbolic Function Type
  
Symbolic Function Type
If you select Symbolic in the Function Definition dialog box, as the type for your function, you type an algebraic expression in the Symbolic entry box. Click Available Function Components to access the Symbolic Options dialog box. This dialog box contains the following:
Independent variables
Constants, operators, and functions, that are also available on the Symbolic Options dialog box.
The algebraic expression cannot include another function or refer to the same function.
The following is an example of a function:
if (time<10, sin (pi*time/5), 0)
For all functions, if you click the independent variable in the Variables box and the other symbols in their respective boxes, Creo Simulate places them in the Symbolic entry box. You can also type in the expression, using the Valid Symbols table as a guide.
 
* For material properties, the only valid independent variable is temperature.