Produce an output token on each firing with a value that is
equal to the specified math function of the input.
The input and output types are DoubleToken. The functions
are a subset of those in the java.lang.Math class. They are:
<ul>
<li> <b>exp</b>: The exponential function.
This is the default function for this actor
If the argument is NaN, then the result is NaN.
<li> <b>log</b>: The natural logarithm function.
If the argument is NaN, then the result is NaN.
<li> <b>sign</b>: If the argument is greater than 0, return 1.0, if
it is less than 0, return -1.0, otherwise return 0.0.
<li> <b>square</b>: The square function
If the argument is NaN, then the result is NaN.
<li> <b>sqrt</b>: The square root function.
If the argument is NaN, then the result is NaN.
</ul>
<p>
C. Fong, Steve Neuendorffer
$Id: UnaryMathFunction.java 70398 2014-10-22 23:44:32Z cxh $
Ptolemy II 4.1
Yellow (neuendor)
Red (neuendor)
The function to compute. This is a string-valued attribute
that defaults to "exp".