Ehrenfest's urn

[Didier Lachieze]

(12-29-2021 11:53 PM)zahi48g Wrote:  it does not try to remove L2(2) from L2 but n from L2 .

With SUPPRESS(L2,n) you are removing from L2 the element at the nth position, so if L2={2} then SUPRESS(L2,2) will fail because there is only one element in the list. The correct instruction to remove 2 from the list is SUPPRESS(L2,POS(L2,2))) which will remove 2 from the list whatever it’s position in the list.

(12-29-2021 11:53 PM)zahi48g Wrote:  If you get these results , could copy and paste you code ?

Here is a working code, I’ve added the number of elements in the urns as a parameter of the program so you can test with more than two:

Code:

#pragma mode( separator(.,;) integer(h32) )

EXPORT EHRENFEST1(N)
BEGIN
 LOCAL n,p,K;
 INPUT(p);
 L1:=MAKELIST(I,I,1,N);
 L2:={};
 FOR K FROM 1 TO p DO
  n:=RANDINT(1,N);
  IF POS(L1,n) THEN
   L1:=SUPPRESS(L1,POS(L1,n));
   L2(0):=n;
  ELSE
   L2:=SUPPRESS(L2,POS(L2,n));
   L1(0):=n;
  END;
 END;
 PRINT(SORT(L1));
 PRINT(SORT(L2));
END;