The alternative room is used for scheduling lessons if the room originally desired is already booked. In our example SH1 is the alternative room of SH2 (and vice versa).
Rings of alternative rooms
You may string functionally equivalent rooms together in such a way that that they form a ring of alternative rooms. This has already been entered in the example. The alternative room for R1a is R1b, the one for R1b is R2a and so on until the ring is closed.
If, during an optimisation run, it turns out that the desired room for a lesson (e.g. R1b) is already occupied, then the next rooms in the ring (R2a ...) will be checked until a free room is found in the ring.
These rings of alternative rooms make it possible to easily model the "geographical" circumstances of the school by having the sequence of alternative rooms reflect the position of the individual rooms to each other.You can thus save teachers and students wasting time moving between rooms when the neighbouring rooms are located next to each other in the ring.