49 lines
1.1 KiB
Perl
49 lines
1.1 KiB
Perl
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% simple constraint solver for inequalities between variables
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% thom fruehwirth ECRC 950519, LMU 980207, 980311
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:- use_module( library(chr)).
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handler leq.
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constraints leq/2.
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% X leq Y means variable X is less-or-equal to variable Y
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:- op(500, xfx, leq).
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reflexivity @ X leq X <=> true.
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antisymmetry @ X leq Y , Y leq X <=> X=Y.
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idempotence @ X leq Y \ X leq Y <=> true.
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transitivity @ X leq Y , Y leq Z ==> X leq Z.
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/*
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% more efficient, less propagating version using pragma passive
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reflexivity @ X leq X <=> true.
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antisymmetry @ X leq Y , Y leq X # Id <=> X=Y pragma passive(Id).
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idempotence @ X leq Y # Id \ X leq Y <=> true pragma passive(Id).
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transitivity @ X leq Y # Id , Y leq Z ==> X leq Z pragma passive(Id).
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*/
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% this generates a circular leq-relation chain with N variables
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time(N):-
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cputime(X),
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length(L,N),
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genleq(L,Last),
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L=[First|_],
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Last leq First,
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cputime( Now),
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Time is Now-X,
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write(N-Time), nl.
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genleq([Last],Last).
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genleq([X,Y|Xs],Last):-
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X leq Y,
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genleq([Y|Xs],Last).
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cputime( Ts) :-
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statistics( runtime, [Tm,_]),
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Ts is Tm/1000.
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% eof handler leq -----------------------------------------------
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