In general, there are many ways to express the same linear relationship
between variables. clp(Q,R) does not care to distinguish between
them, but the user might. The predicate
ordering(
+Spec)
gives you some control over the
variable ordering. Suppose that instead of B, you want
Mp to be the defined variable:
clp(r) ?- mg(P,12,0.01,B,Mp). {B=1.1268250301319698*P-12.682503013196973*Mp}This is achieved with:
clp(r) ?- mg(P,12,0.01,B,Mp), ordering([Mp]). {Mp= -0.0788487886783417*B+0.08884878867834171*P}One could go one step further and require P to appear before (to the left of) B in an addition:
clp(r) ?- mg(P,12,0.01,B,Mp), ordering([Mp,P]). {Mp=0.08884878867834171*P-0.0788487886783417*B}
Spec in ordering(
+Spec)
is either a list of
variables with the intended ordering, or of the form
A
<
B. The latter form means that A goes to the
left of B. In fact,
ordering([A,B,C,D])
is shorthand for:
ordering(A < B), ordering(A < C), ordering(A < D), ordering(B < C), ordering(B < D), ordering(C < D)
The ordering specification only affects the final presentation of the
constraints. For all other operations of clp(Q,R), the ordering is immaterial.
Note that ordering/1
acts like a constraint: you can put it anywhere
in the computation, and you can submit multiple specifications.
clp(r) ?- ordering(B < Mp), mg(P,12,0.01,B,Mp). {B= -12.682503013196973*Mp+1.1268250301319698*P} clp(r) ?- ordering(B < Mp), mg(P,12,0.01,B,Mp), ordering(P < Mp). {P=0.8874492252651537*B+11.255077473484631*Mp}