LOGO-L> Randomly Chosen Balls 
Author Message
 LOGO-L> Randomly Chosen Balls

Hello everyone,

I hope you'll have a good week-end and this little problem may be brings
you some fun.

It has a gas behaviour background. Specialists will describe all this
better, I'll just say, that the suggested program describes the
Ehrenfest model.
Given two jugs. One initially is filled with the numbered (1 through n)
bals, the other is empty. There is also a box with numbered (1--n)
tickets. One randomly choose the ticket, reads it's number and puts it
back into the box. Then he takes a ball with that number from one jug
and puts it into the other. He repeats this actions many times.
The question is to describe the quantity change of the balls in both

It might be solved in Logo with the using just one list for balls. The
balls in one jug are marked with 1, in the other -- with -1.
Diagrams are drawn after  50th, 100th, 150th, etc., balls are chosen.

This is my suggestion:
to balls.main
pr [please, give the number of balls]
make "n rw
make "a []
balls.process 1

to balls.form
; initial "filling" of the jug
repeat :n [make "a lput 1 :a]

to balls.process :ncount
; the ball with the chosen number changes it's jug.
invert 1+randm :n
if (remainder :ncount 50) = 0 ~
   [balls.diagramma (:n+balls.summa)/2 (:n-balls.summa)/2]
balls.process :ncount+1

to balls.summa
make "s 0
repeat :n [make "s :s+item repcount :a]
op :s

to invert :i
repeat :i-1[make "a bf lput first :a :a]
make "a bf lput -1*first :a :a
repeat :n-:i[make "a bf lput first :a :a]

to balls.diagramma :x :y
pu setxy -30 0 setpensize [15 15] setpc [255 0 0]
pd fd :x/:n*200
pu setxy 30 0 setpensize [15 15] setpc [0 0 255]
pd fd :y/:n*200


I know at least one person, who will do it much better. :-)
I'm curious to know -- how?


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Tue, 04 Apr 2000 03:00:00 GMT  
 LOGO-L> Randomly Chosen Balls


>to invert :i
>repeat :i-1[make "a bf lput first :a :a]
>make "a bf lput -1*first :a :a
>repeat :n-:i[make "a bf lput first :a :a]

This sounds like another candidate for an array.

make "a array :n

to invert :i
setitem :i :a (- (item :i :a))

Also consider using TRUE and FALSE instead of 1 and -1 as the
values to store; then you can say things like

if (item :i :a) [...]

You'd change INVERT to use NOT instead of -.

Wed, 05 Apr 2000 03:00:00 GMT  
 [ 2 post ] 

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