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.