initializeDefaultStrategy - Implement this method in derived classes to
specify the contents (possibly null) of the default Strategy using the
addDefaultAlgorithm(Class,AlgorithmClass) method.
Classes that implement this interface can be used to generate absolute
elastic scattering cross sections and to generate randomized angles generated
from the partial cross section.
isDerivedFrom - Is this spectrum derived from the argument spectrum?
(Recursively checks the whole chain of derivation if this derived spectrum
is derived from yet another.)