PTOLEMY II - CiteSeerX

3.3.3 String Parameters
Expressions
Some parameters have values that are always strings of characters. Such parameters support a simple
string substitution mechanism where the value of the string can reference other parameters in scope
by name using the syntax $name, where name is the name of the parameter in scope. For example, the
StringCompare actor in figure 3.4 has as the value of firstString “The answer is $PI”. This references
the built-in constant PI. The value of secondString is “The answer is 3.1415926535898”. As shown in
the figure, these two strings are deemed to be equal because $PI is replaced with the value of PI.
3.3.4 Expression Actor
The Expression actor is a particularly useful actor found in the math library. By default, it has one
output and no inputs, as shown in Figure 3.5(a). The first step in using it is to add ports, as shown in (b)
and (c), resulting in a new icon as shown in (d). Note: In (c) when you click on Add, you will be
prompted for a Name (pick one) and a Class. Leave the Class entry blank and click OK. You then
specify an expression using the port names, as shown in (e), resulting in the icon shown in (f).
FIGURE 3.3. Sinewave actor, showing its port parameters, and their use at the lower level of the hierarchy.
100 Ptolemy II