Made the lib function into a pure numpy array calculation.
This requires, that r20a, r20b and dw has same dimension as the dispersion points.
Task #7807 (https://gna.org/task/index.php?7807): Speed-up of dispersion models for Clustered analysis.
Authored by: tlinnet 2014-06-11
Parent: [r23839]
Child: [r23841]