perm.h – permutations¶
Memory management¶
-
slong *_perm_init(slong n)¶
Initialises the permutation for use.
-
void _perm_clear(slong *vec)¶
Clears the permutation.
Assignment¶
-
void _perm_set(slong *res, const slong *vec, slong n)¶
Sets the permutation
res
to the same as the permutationvec
.
-
void _perm_set_one(slong *vec, slong n)¶
Sets the permutation to the identity permutation.
-
void _perm_inv(slong *res, const slong *vec, slong n)¶
Sets
res
to the inverse permutation ofvec
. Allows aliasing ofres
andvec
.
Composition¶
-
void _perm_compose(slong *res, const slong *vec1, const slong *vec2, slong n)¶
Forms the composition \(\pi_1 \circ \pi_2\) of two permutations \(\pi_1\) and \(\pi_2\). Here, \(\pi_2\) is applied first, that is, \((\pi_1 \circ \pi_2)(i) = \pi_1(\pi_2(i))\).
Allows aliasing of
res
,vec1
andvec2
.
Parity¶
-
int _perm_parity(const slong *vec, slong n)¶
Returns the parity of
vec
, 0 if the permutation is even and 1 if the permutation is odd.
Randomisation¶
-
int _perm_randtest(slong *vec, slong n, flint_rand_t state)¶
Generates a random permutation vector of length \(n\) and returns its parity, 0 or 1.
This function uses the Knuth shuffle algorithm to generate a uniformly random permutation without retries.
Input and output¶
-
int _perm_print(const slong *vec, slong n)¶
Prints the permutation vector of length \(n\) to
stdout
.