214 lines
4.4 KiB
Prolog
214 lines
4.4 KiB
Prolog
/*************************************************************************
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* *
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* YAP Prolog *
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* *
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* Yap Prolog was developed at NCCUP - Universidade do Porto *
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* *
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* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
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* *
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**************************************************************************
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* *
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* File: random.yap *
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* Last rev: 5/12/99 *
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* mods: *
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* comments: Random operations *
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* *
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*************************************************************************/
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% original code from RA O'Keefe.
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% This is algorithm AS 183 from Applied Statistics. I also have a C
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% version. It is really very good. It is straightforward to make a
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% version which yields 15-bit random integers using only integer
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% arithmetic.
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/** @defgroup Random Random Number Generator
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@ingroup YAPLibrary
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@{
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The following random number operations are included with the
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`use_module(library(random))` command. Since YAP-4.3.19 YAP uses
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the O'Keefe public-domain algorithm, based on the "Applied Statistics"
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algorithm AS183.
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@pred getrand(- _Key_)
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Unify _Key_ with a term of the form `rand(X,Y,Z)` describing the
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current state of the random number generator.
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*/
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/** @pred random(+ _LOW_, + _HIGH_, - _NUMBER_)
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Unify _Number_ with a number in the range
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`[LOW...HIGH)`. If both _LOW_ and _HIGH_ are
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integers then _NUMBER_ will also be an integer, otherwise
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_NUMBER_ will be a floating-point number.
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*/
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/** @defgroup Pseudo_Random Pseudo Random Number Integer Generator
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@ingroup YAPLibrary
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@{
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The following routines produce random non-negative integers in the range
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0 .. 2^(w-1) -1, where w is the word size available for integers, e.g.
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32 for Intel machines and 64 for Alpha machines. Note that the numbers
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generated by this random number generator are repeatable. This generator
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was originally written by Allen Van Gelder and is based on Knuth Vol 2.
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*/
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/** @pred random(- _Number_)
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Unify _Number_ with a floating-point number in the range `[0...1)`.
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*/
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/** @pred randseq(+ _LENGTH_, + _MAX_, - _Numbers_)
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Unify _Numbers_ with a list of _LENGTH_ unique random integers
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in the range `[1... _MAX_)`.
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*/
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/** @pred randset(+ _LENGTH_, + _MAX_, - _Numbers_)
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Unify _Numbers_ with an ordered list of _LENGTH_ unique random
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integers in the range `[1... _MAX_)`.
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*/
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/** @pred setrand(+ _Key_)
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Use a term of the form `rand(X,Y,Z)` to set a new state for the
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random number generator. The integer `X` must be in the range
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`[1...30269)`, the integer `Y` must be in the range
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`[1...30307)`, and the integer `Z` must be in the range
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`[1...30323)`.
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*/
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:- module(random, [
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random/1,
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random/3,
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randseq/3,
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randset/3,
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getrand/1,
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setrand/1
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]).
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:- use_module(library(pairs)).
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:- use_module(library(error)).
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:- use_module(library(lists)).
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:- load_foreign_files([yap_random], [], init_random).
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% random(R) binds R to a new random number in [0.0,1.0)
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% random(L, U, R) binds R to a random integer in [L,U)
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% when L and U are integers (note that U will NEVER be generated),
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% or to a random floating number in [L,U) otherwise.
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random(L, U, R) :-
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( integer(L), integer(U) ->
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U > L,
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random(X),
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R is L+integer((U-L)*X)
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;
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number(L), number(U),
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U > L,
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random(X),
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R is L+((U-L)*X)
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).
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/* There are two versions of this operation.
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randset(K, N, S)
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generates a random set of K integers in the range 1..N.
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The result is an ordered list, such as setof might produce.
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randseq(K, N, L)
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generates a random sequence of K integers, the order is as
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random as we can make it.
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*/
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randset(K, N, S) :-
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K >= 0,
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K =< N,
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randset(K, N, [], S).
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randset(0, _, S, S) :- !.
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randset(K, N, Si, So) :-
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random(X),
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X * N < K, !,
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J is K-1,
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M is N-1,
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randset(J, M, [N|Si], So).
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randset(K, N, Si, So) :-
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M is N-1,
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randset(K, M, Si, So).
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randseq(K, N, S) :-
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randseq(K, N, L, []),
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keysort(L, R),
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strip_keys(R, S).
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randseq(0, _, S, S) :- !.
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randseq(K, N, [Y-N|Si], So) :-
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random(X),
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X * N < K, !,
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random(Y),
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J is K-1,
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M is N-1,
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randseq(J, M, Si, So).
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randseq(K, N, Si, So) :-
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M is N-1,
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randseq(K, M, Si, So).
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strip_keys([], []) :- !.
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strip_keys([_-K|L], [K|S]) :-
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strip_keys(L, S).
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setrand(rand(X,Y,Z)) :-
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integer(X),
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integer(Y),
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integer(Z),
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X > 0,
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X < 30269,
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Y > 0,
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Y < 30307,
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Z > 0,
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Z < 30323,
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setrand(X,Y,Z).
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getrand(rand(X,Y,Z)) :-
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getrand(X,Y,Z).
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