connections among distant sequences
Wouter Meeussen
wouter.meeussen at pandora.be
Mon Feb 11 00:15:42 CET 2002
in some of the stuff below, it can be argued that
a single "strategy" connects distant sequences.
Maybe arbitrary, maybe original & productive.
(cum grano salis)
Consider all possible combinations of two-argument
functions P,Q and R, wraped around their arguments
a,b,c and d, as in
P[a, Q[b, R[c, d]]]
P[a, Q[R[b, c], d]]
P[Q[a, b], R[c, d]]
P[Q[a, R[b, c]], d]
P[Q[R[a, b], c], d]
the 5 results represent the five "bracketings"
with 3 sets of brackets (= 3 functions).
(bracketings are counted by Catalans, or binary trees).
Same thing can be done for w=1 ... 6 or more functions
with (w+1) arguments, but calculations get nasty & slow.
And now for some counting.
You'll notice that both functions and arguments remain
"in sequence" (please pardon this cheap pun).
What if we replace the functions with functions A or B,
in all 2^w combinations,
PQR -> AAA,AAB,ABA,ABB,BAA,BAB,BBA,BBB.
and, to top that, we present the arguments in any order,
effectively generating all permutations of them.
What can this result be called?
"
All possible outcomes of applying the functions A and\or B
warped w times on the w+1 arguments a[1] ... a[w+1]
"
Now, imagine that functions A and B have no special nice properties,
Then every result is different, and we easily count the *different*
results as function of w: 2^w cat[w] (w+1)!
or {4,48,960,26880,967680, 42577920}=A052714=(2w)!/w! 2^w
BUT
the functions A and B can be given the properties of associativity
and commutativity, or "flat-ness" and "orderless-ness",
the first implying A[b,A[b,a]] equals A[b, b, a]
the second means A[b,a] equals A[a,b] as you all know.
RESULTS:
{function A} {function B} w={1, 2,3 , 4}
{nil} {nil} {4,48,960,26880} A052714
{Orderless} {nil} {3,27,405, 8505,229635} A011781
{Orderless} {Orderless} {2,12,120, 1680,30240} A001813
{Flat} {nil} {4,42,744,18480} do not match anything
{Flat} {Orderless} {3,21,249, 4155} do not match anything
{Flat,Orderless}{nil} {3,25,351, 6901} do not match anything
{Flat,Orderless}{Orderless} {2,10, 86, 1036} do not match anything
{Flat} {Flat} {4,36,528,10800} A052716
{Flat,Orderless}{Flat} {3,19,195, 2791} A053554 A048172
{Flat,Orderless}{Flat,Orderless} {2, 8, 52, 472} A006351
A052714 by encyclopedia at pommard.inria.fr, Jan 25 2000
A011781 by killough at wagner.convex.com (Lee D. Killough)
A001813 by njas & James A. Sellers (sellersj at math.psu.edu), May 01 2000
A052716 by encyclopedia at pommard.inria.fr, Jan 25 2000
A053554 by njas, Jan 16 2000
A048172 by njas
A006351 by njas
---------------------------------------------------
If we drop the (w+1)! permutations of the arguments,
and only keep the cat[w] parentesizations of the functions,
w instances of A and b, then we get
{nil} {nil}
{Orderless} {nil}
{Orderless} {Orderless}
are all {28,40,224,1344,8448,54912} A052701
=cat[w]2^w
{Flat} {nil}
{Flat} {Orderless}
{Flat,Orderless}{nil}
are all {2,7,31,154,820,4575,26398} A007863
{Flat} {Flat}
{Flat,Orderless}{Flat}
are both {2,6,22,90,394,1806,8558} A006318
=2* A001003
---------------------------------------------------
needless to say that fitting to a sequence, using a 4 term match,
should be called "poor & unsafe".
Maybe someone with brains & training could have a peek at this?
"in obscuritate finio" ;-)
wouter.meeussen at pandora.be
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