The problem was that is "sparse" is not const, then sparse.diagonal() must have the
LValueBit flag meaning that sparse.diagonal().coeff(i) must returns a const reference,
const Scalar&. However, sparse::coeff() cannot returns a reference for a non-existing
zero coefficient. The trick is to return a reference to a local member of
evaluator<SparseMatrix>.
- Dynamic is now an invalid value
- introduce a HugeCost constant to be used for runtime-cost values or arbitrarily huge cost
- add sanity checks for cost values: must be >=0 and not too large
This change provides several benefits:
- it fixes shortcoming is some cost computation where the Dynamic case was not properly handled.
- it simplifies cost computation logic, and should avoid future similar shortcomings.
- it allows to distinguish between different level of dynamic/huge/infinite cost
- it should enable further simplifications in the computation of costs (save compilation time)
