Member SurfpackApproximation::build () override: Right now, we're completely deleting the old data and then recopying the current data into a SurfData object. This was just the easiest way to arrive at a solution that would build and run. This function is frequently called from addPoint rebuild, however, and it's not good to go through this whole process every time one more data point is added.
Member SurfpackApproximation::hessian (const Variables &vars) override: Make this acceptably efficient
Member SurfpackApproximation::hessian (const RealVector &c_vars) override: Make this acceptably efficient