Re: [tlaplus] Re: Write custom java code function plug-in for PLUSCAL/TLA to compute combinations on sequences w/ dups?

I believe that the post [1] on StackOverflow, with a link to a worked-out example on GitHub, should help you get started.

If I understand correctly, the TLA+ specification of your operator would be

Range(s) == { s[i] : i \in DOMAIN s }

RECURSIVE PermSeqs(_,_)

\* set of sequences of length k that are permutations of elements of sequence s
PermSeqs(s,k) ==
IF k=0 THEN { << >> }
ELSE { t \in [1..k -> Range(s)] : \E i \in 1 .. Len(s) :
/\ Head(t) = s[i]
/\ Tail(t) \in PermSeqs(SubSeq(s,1,i-1) \o SubSeq(s,i+1,Len(s)), k-1) }

For example,

PermSeqs(<<1,2,2,3,4>>, 2) =

{ <<1, 2>>, <<1, 3>>, <<1, 4>>,

<<2, 1>>, <<2, 2>>, <<2, 3>>, <<2, 4>>,
<<3, 1>>, <<3, 2>>, <<3, 4>>,
<<4, 1>>, <<4, 2>>, <<4, 3>> }

PermSeqs(<<1,2>>, 3) = {}

Stephan

[1] https://stackoverflow.com/questions/53908653/use-module-overloading-to-implement-a-hash-function-in-tla

On 6 Mar 2019, at 01:54, 7532yahoo@xxxxxxxxx wrote:

On Tuesday, March 5, 2019 at 7:47:16 PM UTC-5, 7532...@gmail.com wrote:
The built-in Permutations works on sets. I need to generate all combinations on a sequence of length N take k. The sequence may have duplicates.

I could code this in PLUSCAL, however, where might I look to see how I can write some JAVA code to do same where it might be easier, and then call it from TLA?

Thank you in advance for all the help I've gotten on this chat! Definitely value-add.

Correction: permutations not combinations...

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