Created the ability to check if a vector is empty.
added function at the poptea level that updates the model data.  I setup it up so that it updates it based on an input. This reduces the need to recalculate.
deleted blank space
For the initialization of poptea, the model predictions are now updated at the moment of creation.
Created method to calculate the sDerivative.  This can be used to verify the solution is at the minimum.