Require one item to come before another

precede(P, before, after) requires item before to be in an earlier slot of the permutation P than item after: a pickup before its delivery, or a job before the job that needs its output. The service only considers arrangements that meet the requirement, so every solution meets it.

Usage

precede(P, before, after)

Arguments

P

A permutation from perm_var().

before, after

Items: whole numbers from 1 to the size of the permutation.

Value

The permutation, invisibly.

Details

precede() may be called several times for one permutation. Requirements that contradict each other, such as 1 before 2 and 2 before 1, are an error.

Examples

m <- model()
route <- perm_var(m, "route", 5)
precede(route, 4, 1)                # stop 4 is visited before stop 1
precede(route, 2, 5)                # and stop 2 before stop 5