In principle this function calls its counterpart in builder_and_solver and scheme but before if it is necessary the new set of DOFs to be solved in this iteration is identified and related changes are done by following functions of builder_and_solver: SetUpDofSet, SetUpSystem and ResizeAndInitializeVectors.
what do the initializesolutionstep of builder_and_solver and scheme do? I have no example for builder_and_solver. I'm using residulabased_elimination_builder_and_solver and this function does nothing but for scheme, for example Bossak, it does something. It calls initializesolutionstep of the Scheme that calls this function for element and condition and also calculate some constants for Bossak scheme.