Beefy Boxes and Bandwidth Generously Provided by pair Networks
Come for the quick hacks, stay for the epiphanies.
 
PerlMonks  

Re^4: Obtaining terms in an expansion

by pKai (Priest)
on Jan 06, 2006 at 19:34 UTC ( [id://521606]=note: print w/replies, xml ) Need Help??


in reply to Re^3: Obtaining terms in an expansion
in thread Obtaining terms in an expansion

Thank you, for pointing me to the "factorial"
Note to self: Don't transfer mathematical/technical terms from German to English without consulting a dictionary first.

Also, would you be able to give example code for the subset iteration with Math::Combinatorics?

If there is an easy way to do so, it has escaped me.

The closest I saw in the docs was that example to generate:
"Morse signals: diferent signals of 3 positions using the two symbols - and .".

Now Morse signals of length 3 are surely one-to-one and onto the subsets of a 3 element set (set elements = pos in signal; element not/contained = dot/dash)

The given iteration using next_multiset and next_string is like computing 2**n as sumk=0..n nCk

At least this is not trivial application of the modules methods.

Replies are listed 'Best First'.
Re^5: Obtaining terms in an expansion
by ivancho (Hermit) on Jan 06, 2006 at 22:19 UTC
    I guess that's as good as it gets from Math::Combinatorics - doable, but not very natural.

    There are plenty of other iterators out there that give all the subsets, though - List::PowerSet, Data::PowerSet, Algorithm::ChooseSubsets - We just have to convert them to give a bit mask instead - ie:

    use List::PowerSet qw/powerset_lazy/;
my @set = (0) x $N;
my @C   = (1) x 2**$N;
my $M = 0;
my $ps_itr = powerset_lazy(0 .. $N-1);
while (my $ref_set = $ps_itr->()) {
    $_ = 1 for local @set[@$ref_set];
    $C[ $M ] *= $arr->[ $_ ][ $set[$_] ] for 0 .. $N-1;
    $M++;
}

    [download]
[reply]
[d/l]
Re^5: Obtaining terms in an expansion
by DungeonKeeper (Novice) on Jan 09, 2006 at 10:09 UTC
    The 2**N doesn't need to be computed anyway. next_multiset() will just keep returning each possible set until all have been returned, at which point it returns undef().

    Everything but the troll

[reply]

In Section Seekers of Perl Wisdom

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?

www.com | www.net | www.org
Node Status?
node history
Node Type: note [id://521606]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? • Last hour • Other CB clients
Other Users?
Others pondering the Monastery: (None)
    As of 2024-04-19 00:00 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      No recent polls found