The following command indirectly calls the IDL function SQRT (the square root function) with an argument of 4 and stores the result in the variable R:
R = CALL_FUNCTION('SQRT', 4)
Result = CALL_FUNCTION(Name [, P1, ..., Pn])
The result of the called function (specified by the string Name) is passed back as the result of this routine.
A string containing the name of the function to be called. This argument can be a variable, which allows the called function to be determined at runtime.
The arguments to be passed to the function given by Name. These arguments are the positional and keyword arguments documented for the called function, and are passed to the called function exactly as if it had been called directly.