Change the initialization and reinitialization policy of the solution
vector. Values are:

* `bastert`: for each variable (or at `init-random` rate) use cost values to set
  or unset variable.
* `pessimistic-solve`: found a solution for each (or at `init-random` rate)
  constraints. For soft constraints, affect one to strict minimum variables.
* `optimistic-solve`: found a solution for each (or or `init-random` rate)
  constraints. For soft constraints, affect one to the maximum variables that
  valid the constraint.
* `cycle` (default): Only for the optimization mode, start with the
  `pessimistic-solve` mode and change to `bastert` then `pessimistic-solve`
  mode. The change between mode is done if and only if three times, optimization
  fails to improve the current solution.