Vaggelis Papoutsis authored Jul 18, 2023 and Andrew Heather committed Dec 18, 2023

Parts of the adjoint optimisation library were re-designed to generalise
the way sensitivity derivatives (SDs) are computed and to allow easier
extension to primal problems other than the ones governed by
incompressible flows. In specific:
- the adjoint solver now holds virtual functions returning the part of
  SDs that depends only on the primal and the adjoint fields.
- a new class named designVariables was introduced which, apart from
  defining the design variables of the optimisation problem and
  providing hooks for updating them in an optimisation loop, provides
  the part of the SDs that affects directly the flow residuals (e.g.
  geometric variations in shape optimisation, derivatives of source
  terms in topology optimisation, etc). The final assembly of the SDs
  happens here, with the updated sensitivity class acting as an
  intermediate.

With the new structure, when the primal problem changes (for instance,
passive scalars are included), the ...