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Re: For Loop and Array related

  • To: mathgroup at
  • Subject: [mg58002] Re: For Loop and Array related
  • From: "Mariusz Jankowski" <mjankowski at>
  • Date: Thu, 16 Jun 2005 05:36:00 -0400 (EDT)
  • Organization: University of Southern Maine
  • References: <d8oucl$t6q$>
  • Sender: owner-wri-mathgroup at

Strange indeed! However, the following gives a consistent total; in the body
of the loop assign Random to a temporary variable

n = Random[Integer,{1,100}];

Also, the Do-loop construct is faster than For, ... and simpler, and if you
need more speed use function Compile.


>>> mchangun at<mchangun at> 06/15/05 6:03 AM >>>
Hi All,

I have an array with 100 elements, all set to zero initially.  Then I
want to randomly choose one element and increase its value by one, and
repeat this 16000 times. Here is my code:

Lattice = Table[0, {n, 100}];
For[i = 1, i = 16000, i++, Lattice[[Random[Integer, {1, 100}]]]++]

So now if I add all the elements in the list Lattice together, I should
get 16000 (I use Total[Lattice] to get the sum of the list).  But this
doesn't happen, and strangely, each time I run this, the sum of the
list is different!  What am I doing wrong?

Also I'm aware that a lot of Mathematica newbies try and write code
like it were C++ and I think i've fallen into this trap as well.  So is
there a different (more Mathematica) way which I can implement the

Thanks in advanced.

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