Symbolic Combinations and Permutations question.

01122015, 07:38 PM
Post: #1




Symbolic Combinations and Permutations question.
Hello everybody,
Is there a function in xCAS or HPPL that outputs combinations (permutations) of all elements in a list. For example: when I have list {1,2,3} and I want combs. of all elements taken two at a time the functions outputs list {{1,2},{1,3},{2,3}} as combinations. Cheers 

01132015, 01:17 AM
Post: #2




RE: Symbolic Combinations and Permutations question.
I don't know of any one builtin command that would do that, but the Prime, being fully programmable, allows you do something along these lines
EXPORT YOURNAME(n) BEGIN LOCAL a,l:={},ll:={},j:=1,k:=1; a:=SIZE(n); FOR j FROM 1 TO a1 DO FOR k FROM j+1 TO a DO l:={{n(j),n(k)}}; ll:=CONCAT(ll,l); END; END; RETURN ll; END; This will give you your desired pairs of combinations, and the code can be extended to return triplets, quadruplets, etc. 

01132015, 02:09 AM
Post: #3




RE: Symbolic Combinations and Permutations question.
(01132015 01:17 AM)Helge Gabert Wrote: I don't know of any one builtin command that would do that, but the Prime, being fully programmable, allows you do something along these lines Thank you Helge Gabert, I will modify it to work as nchoosek i matlab so you can give two arguments; list of elements an the number elements to choose. Cheers 

01132015, 02:53 AM
(This post was last modified: 01132015 03:53 AM by Han.)
Post: #4




RE: Symbolic Combinations and Permutations question.
Here's my attempt at the general version via recursion. Usage:
COMBOSET(list,n) Works for arbitrary sets, too. For example, try: COMBOSET({"a","b",1,[0,1,0]},2) Code: EXPORT COMBOSET(s,n) Graph 3D  QPI  SolveSys 

01132015, 03:57 AM
Post: #5




RE: Symbolic Combinations and Permutations question.
(01132015 02:53 AM)Han Wrote: Here's my attempt at the general version via recursion. Usage: Hello Han, Thank you. I do not think I could make i better. I've written similar program for HP50 and recently was thinking to rewrite it for HP Prime. I was thinking about your resent post about solving system of eqs. You described case were there was more eqs. than unknowns and fsolve was giving some kind of error. If I remember correctly from linear algebra system like that is called overdetermined and theoretically could have only one solution but mostly has number of solutions for different combinations of eqs. for example if you have 3 eqs. and 2 unknowns you would have, in general, 3 solutions: sol. for eq1 and eq2, sol. for eq1 and eq3 and sol. for eq2 and eq3 (combinations of eqs.). but I have to find the book and do some reviewing. Thanks once again. Cheers 

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