Supersedes https://git.dynare.org/Dynare/dynare/issues/564 and is related to https://git.dynare.org/Dynare/dynare/issues/1678 See also https://forum.dynare.org/t/evaluate-planner-objective-in-non-linear-model/15492 Remaining: - [x] fixing or documenting the regression in behavior introduced in e880d1bc. In contrast to previous behavior `histval` will be ignored. `planner_objective_value` now returns conditional and unconditional welfare instead of welfare for different values of the Lagrange multiplier. (done in !1923) - [x] the question of an interface for setting the initial condition (https://git.dynare.org/Dynare/preprocessor/-/issues/64) - [x] Adding higher order results to `evaluate_planner_objective` - [x] Compute unconditional welfare at order>2 - [x] Documenting the recent changes