[Jprogramming] Everyone giving dollars to random others

[Devon McCormick]

So, you start with $10,000 (=100*$100) but end up with $2,025 (=45*$45),
how?

On Mon, Jul 10, 2017 at 3:59 PM, Raul Miller <rauldmiller at gmail.com> wrote:

> I don't really understand what you mean by "mean expectations" - could
> you describe the intent there?
>
> That said, here's how far I've gotten in implementing this concept:
>
>    tick=: (0 >. <:) + i.@# +/@:(=/)~ +/@:* ?@# #
>    (mean,stddev)"1 tick^:(i.10)]100#100
> 100        0
> 100 0.932034
> 100  1.41421
> 100  1.91749
> 100  2.07437
> 100  2.34844
> 100  2.48633
> 100  2.71546
> 100  2.97803
> 100  3.26289
>
> (Also, for animation in J, there's actually a lot of options...
> basically though you set up a paint event which calls into your
> rendering code and then trigger updates from systimer.)
>
> Thanks,
>
> --
> Raul
>
> On Mon, Jul 10, 2017 at 3:43 PM, Xiao-Yong Jin <jinxiaoyong at gmail.com>
> wrote:
> > I thought this is a good lunch break exercise.
> >
> > http://www.decisionsciencenews.com/2017/06/19/counterintuitive-
> problem-everyone-room-keeps-giving-dollars-random-others-
> youll-never-guess-happens-next/
> >
> > Quote: “Imagine a room full of 100 people with 100 dollars each. With
> every tick of the clock, every person with money gives a dollar to one
> randomly chosen other person. After some time progresses, how will the
> money be distributed?”
> >
> > And I came up with this simulation.  (45 people with 45 dollars each,
> same as on the webpage.)
> >
> >  /:~@(-&1`]@.(=&0)"0 (#/.~@] + ~.@]{[)`(~.@])`[} >&0 # (?@#~@#@]`]`[}
> ]I.@:=i.@#)^:_@?@#~@#)^:5000 #~45
> >
> > And I really like to see the mean expectations and the standard
> deviation of the mean, I ended up doing this.  (Make sure the J sentence is
> one long line if you want to try it out.)
> >
> >     ((],.[:(+/%#*<:@#)&.:*: -"1)+/%#)}.(/:~@(-&1`]@.(=&0)"0 (#/.~@] +
> ~.@]{[)`(~.@])`[} >&0 # (?@#~@#@]`]`[} ]I.@:=i.@#)^:_@?@#~@#)^:10000)^:(<65)
> #~45
> > 0.984375 0.124984
> >  2.01562 0.170335
> >   3.0625 0.180765
> >  4.15625 0.230616
> >  5.21875 0.248476
> >   6.1875 0.306894
> >  7.35938 0.332862
> >  8.64062 0.362809
> >  9.84375 0.380723
> >  10.9688 0.383805
> >   12.125 0.407944
> >  13.6406 0.423964
> >  15.0625 0.457453
> >  16.5312 0.462893
> >  18.1875 0.480717
> >  19.7031 0.464877
> >  21.1562 0.475709
> >  22.7031 0.483702
> >  24.4062 0.516935
> >  26.4062   0.5768
> >  28.1094 0.604266
> >  29.8281 0.617838
> >   31.875  0.61942
> >  33.9375 0.603345
> >  35.7812 0.642211
> >  37.9844 0.647987
> >  40.6562 0.731321
> >       43 0.739342
> >  45.3906 0.723616
> >  48.0469   0.7613
> >  51.6094 0.823639
> >  54.7656 0.873934
> >  57.1406 0.815544
> >       60 0.866598
> >  63.8594 0.898319
> >    68.75 0.918018
> >  73.5781  1.00736
> >  78.3281  1.08128
> >  84.9688  1.25534
> >  93.4688  1.29731
> >  104.578  1.73274
> >  114.922  2.07574
> >  131.938   2.7357
> >  159.359  4.40899
> >  204.766  7.24239
> >
> > So, how do I make a fancy animation (like the one in the webpage I
> linked in the beginning of this message) with J?
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>



-- 

Devon McCormick, CFA

Quantitative Consultant