This is indeed a bug! Thanks for the report.
The thing is that the code for cardinality (before the call to .list())
is inherited from permutations without a fixed length. The (wrong)
number you got (1680) is actually the number of permutations without
length restriction.
See
http://trac.sagemath.org/ticket/20317
By the way you would better use Permutations(ms, 3) rather than
importing Permutations_msetk.
Vincent
On 29/03/16 09:41, Karol Suchan wrote:
Hi,
I've spotted a strange behaviour of Permutations.cardinality(): first it
reports a weird number, but after a call to list() it gets ok. Any reason
why?
I copy a code that compares the behaviour of Tuples, Permutations and
Arrangements.
%%%%%%%%%%%%%%%
from sage.combinat.permutation import *
from sage.combinat.tuple import *
ms=[1,1,1,2,2,2,3,3,3]
tms = Tuples(ms,3)
pms = Permutations_msetk(ms,3)
ams = Arrangements_msetk(ms,3)
print("ctms: " + str(tms.cardinality()))
print("cpms: " + str(pms.cardinality()))
print("cams: " + str(ams.cardinality()))
print("ltms: " + str(tms.list()))
print("lpms: " + str(pms.list()))
print("lams: " + str(ams.list()))
print("ctms: " + str(tms.cardinality()))
print("cpms: " + str(pms.cardinality()))
print("cams: " + str(ams.cardinality()))
%%%%%%%%%%%%%%%
Best,
Karol
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