constructor from an ordered pair of PoolName (string like) objects and a function with the set of formal argument names forming a subset of the state_variable_names
# S4 method for `function`,character,character,missing
InternalFlux_by_PoolName(func, sourceName, destinationName)
object of class:function
, A real valued function describing the flux (mass/time)
as function of (some of ) the state variables and time.
object of class:character
, A string identifying the source pool of the flux
object of class:character
, A string identifying the destination pool of the flux