random.pl -- 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.
- random(-R:float) is det
- Binds R to a new random float in the open interval (0.0,1.0).
- 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(+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).
- 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. - maybe is semidet
- Succeed/fail with equal probability (variant of maybe/1).
- maybe(+P) is semidet
- Succeed with probability P, fail with probability 1-P
- maybe(+K, +N) is semidet
- Succeed with probability K/N (variant of maybe/1)
- random_perm2(?A, ?B, ?X, ?Y) is semidet
- Does X=A,Y=B or X=B,Y=A with equal probability.
- 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.
- 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.
- 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.
The implementation uses different techniques depending on the ratio
K/N. For small K/N it generates a set of K random numbers, removes
the duplicates and adds more numbers until |S| is K. For a large K/N
it enumerates 1..N and decides randomly to include the number or
not. For example:
?- randset(5, 5, S). S = [1, 2, 3, 4, 5]. (always) ?- randset(5, 20, S). S = [2, 7, 10, 19, 20].
- 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. Defined as
randseq(K, N, List) :- randset(K, N, Set), random_permutation(Set, List).
- 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.
Undocumented predicates
The following predicates are exported, but not or incorrectly documented.