/* Part of SWI-Prolog
Author: R.A. O'Keefe, V.S. Costa, L. Damas, Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2011-2016, Universidade do Porto, University of Amsterdam,
VU University Amsterdam.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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*/
:- module(random,
[ random/1, % -Float (0,1)
random_between/3, % +Low, +High, -Random
getrand/1, % -State
setrand/1, % +State
maybe/0,
maybe/1, % +P
maybe/2, % +K, +N
random_perm2/4, % A,B, X,Y
random_member/2, % -Element, +List
random_select/3, % ?Element, +List, -Rest
randseq/3, % +Size, +Max, -Set
randset/3, % +Size, +Max, -List
random_permutation/2, % ?List, ?Permutation
% deprecated interface
random/3 % +Low, +High, -Random
]).
:- use_module(library(pairs)).
:- use_module(library(error)).
:- use_module(library(lists)).
/** <module> Random numbers
This library is derived from the DEC10 library random. Later, the core
random generator was moved to C. The current version uses the SWI-Prolog
arithmetic functions to realise this library. These functions are based
on the GMP library.
@author R.A. O'Keefe, V.S. Costa, L. Damas, Jan Wielemaker
@see Built-in function random/1: A is random(10)
*/
check_gmp :-
current_arithmetic_function(random_float),
!.
check_gmp :-
print_message(warning, random(no_gmp)).
:- initialization check_gmp.
/*******************************
* PRIMITIVES *
*******************************/
%! random(-R:float) is det.
%
% Binds R to a new random float in the _open_ interval (0.0,1.0).
%
% @see setrand/1, getrand/1 may be used to fetch/set the state.
% @see In SWI-Prolog, random/1 is implemented by the function
% random_float/0.
random(R) :-
R is random_float.
%! random_between(+L:int, +U:int, -R:int) is semidet.
%
% Binds R to a random integer in [L,U] (i.e., including both L and
% U). Fails silently if U<L.
random_between(L, U, R) :-
integer(L), integer(U),
!,
U >= L,
R is L+random((U+1)-L).
random_between(L, U, _) :-
must_be(integer, L),
must_be(integer, U).
%! random(+L:int, +U:int, -R:int) is det.
%! random(+L:float, +U:float, -R:float) is det.
%
% Generate a random integer or float in a range. If L and U are
% both integers, R is a random integer in the half open interval
% [L,U). If L and U are both floats, R is a float in the open
% interval (L,U).
%
% @deprecated Please use random/1 for generating a random float
% and random_between/3 for generating a random integer. Note that
% random_between/3 includes the upper bound, while this
% predicate excludes it.
random(L, U, R) :-
integer(L), integer(U),
!,
R is L+random(U-L).
random(L, U, R) :-
number(L), number(U),
!,
R is L+((U-L)*random_float).
random(L, U, _) :-
must_be(number, L),
must_be(number, U).
/*******************************
* STATE *
*******************************/
%! setrand(+State) is det.
%! getrand(-State) is det.
%
% Query/set the state of the random generator. This is intended
% for restarting the generator at a known state only. The
% predicate setrand/1 accepts an opaque term returned by
% getrand/1. This term may be asserted, written and read. The
% application may not make other assumptions about this term.
%
% For compatibility reasons with older versions of this library,
% setrand/1 also accepts a term rand(A,B,C), where A, B and C are
% integers in the range 1..30,000. This argument is used to seed
% the random generator. Deprecated.
%
% @see set_random/1 and random_property/1 provide the SWI-Prolog
% native implementation.
% @error existence_error(random_state, _) is raised if the
% underlying infrastructure cannot fetch the random state.
% This is currently the case if SWI-Prolog is not compiled
% with the GMP library.
setrand(rand(A,B,C)) :-
!,
Seed is A<<30+B<<15+C,
set_random(seed(Seed)).
setrand(State) :-
set_random(state(State)).
:- if(current_predicate(random_property/1)).
getrand(State) :-
random_property(state(State)).
:- else.
getrand(State) :-
existence_error(random_state, State).
:- endif.
/*******************************
* MAYBE *
*******************************/
%! maybe is semidet.
%
% Succeed/fail with equal probability (variant of maybe/1).
maybe :-
random(2) =:= 0.
%! maybe(+P) is semidet.
%
% Succeed with probability P, fail with probability 1-P
maybe(P) :-
must_be(between(0.0,1.0), P),
random_float < P.
%! maybe(+K, +N) is semidet.
%
% Succeed with probability K/N (variant of maybe/1)
maybe(K, N) :-
integer(K), integer(N),
between(0, N, K),
!,
random(N) < K.
maybe(K, N) :-
must_be(nonneg, K),
must_be(nonneg, N),
domain_error(not_less_than_zero,N-K).
/*******************************
* PERMUTATION *
*******************************/
%! random_perm2(?A, ?B, ?X, ?Y) is semidet.
%
% Does X=A,Y=B or X=B,Y=A with equal probability.
random_perm2(A,B, X,Y) :-
( maybe
-> X = A, Y = B
; X = B, Y = A
).
/*******************************
* SET AND LIST OPERATIONS *
*******************************/
%! random_member(-X, +List:list) is semidet.
%
% X is a random member of List. Equivalent to random_between(1,
% |List|), followed by nth1/3. Fails of List is the empty list.
%
% @compat Quintus and SICStus libraries.
random_member(X, List) :-
must_be(list, List),
length(List, Len),
Len > 0,
N is random(Len),
nth0(N, List, X).
%! random_select(-X, +List, -Rest) is semidet.
%! random_select(+X, -List, +Rest) is det.
%
% Randomly select or insert an element. Either List or Rest must
% be a list. Fails if List is the empty list.
%
% @compat Quintus and SICStus libraries.
random_select(X, List, Rest) :-
( '$skip_list'(Len, List, Tail),
Tail == []
-> true
; '$skip_list'(RLen, Rest, Tail),
Tail == []
-> Len is RLen+1
),
!,
Len > 0,
N is random(Len),
nth0(N, List, X, Rest).
random_select(_, List, Rest) :-
partial_list(List), partial_list(Rest),
instantiation_error(List+Rest).
random_select(_, List, Rest) :-
must_be(list, List),
must_be(list, Rest).
%! randset(+K:int, +N:int, -S:list(int)) is det.
%
% S is a sorted list of K unique random integers in the range
% 1..N. Implemented by enumerating 1..N and deciding whether or
% not the number should be part of the set. For example:
%
% ==
% ?- randset(5, 5, S).
% S = [1, 2, 3, 4, 5]. (always)
% ?- randset(5, 20, S).
% S = [2, 7, 10, 19, 20].
% ==
%
% @see randseq/3.
% @bug Slow if N is large and K is small.
randset(K, N, S) :-
must_be(nonneg, K),
K =< N,
randset(K, N, [], S).
randset(0, _, S, S) :- !.
randset(K, N, Si, So) :-
random(N) < K,
!,
J is K-1,
M is N-1,
randset(J, M, [N|Si], So).
randset(K, N, Si, So) :-
M is N-1,
randset(K, M, Si, So).
%! randseq(+K:int, +N:int, -List:list(int)) is det.
%
% S is a list of K unique random integers in the range 1..N. The
% order is random. Works as if defined by the following code.
%
% ==
% randseq(K, N, List) :-
% randset(K, N, Set),
% random_permutation(Set, List).
% ==
%
% @see randset/3.
randseq(K, N, S) :-
randseq(K, N, L, []),
keysort(L, R),
pairs_values(R, S).
randseq(0, _, S, S) :- !.
randseq(K, N, [Y-N|Si], So) :-
random(N) < K,
!,
random(Y),
J is K-1,
M is N-1,
randseq(J, M, Si, So).
randseq(K, N, Si, So) :-
M is N-1,
randseq(K, M, Si, So).
%! random_permutation(+List, -Permutation) is det.
%! random_permutation(-List, +Permutation) is det.
%
% Permutation is a random permutation of List. This is intended to
% process the elements of List in random order. The predicate is
% symmetric.
%
% @error instantiation_error, type_error(list, _).
random_permutation(List1, List2) :-
is_list(List1),
!,
random_permutation_(List1, List2).
random_permutation(List1, List2) :-
is_list(List2),
!,
random_permutation_(List2, List1).
random_permutation(List1, List2) :-
partial_list(List1), partial_list(List2),
!,
instantiation_error(List1+List2).
random_permutation(List1, List2) :-
must_be(list, List1),
must_be(list, List2).
random_permutation_(List, RandomPermutation) :-
key_random(List, Keyed),
keysort(Keyed, Sorted),
pairs_values(Sorted, RandomPermutation).
key_random([], []).
key_random([H|T0], [K-H|T]) :-
random(K),
key_random(T0, T).
%! partial_list(@Term) is semidet.
%
% True if Term is a partial list.
partial_list(List) :-
'$skip_list'(_, List, Tail),
var(Tail).
:- multifile
prolog:message//1.
prolog:message(random(no_gmp)) -->
[ 'This version of SWI-Prolog is not compiled with GMP support.'-[], nl,
'Floating point random operations are not supported.'-[]
].