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Re: For Loop and Array related

  • To: mathgroup at
  • Subject: [mg58018] Re: [mg57971] For Loop and Array related
  • From: yehuda ben-shimol <bsyehuda at>
  • Date: Thu, 16 Jun 2005 05:36:57 -0400 (EDT)
  • References: <>
  • Reply-to: yehuda ben-shimol <bsyehuda at>
  • Sender: owner-wri-mathgroup at

The format of the For[] function is
For[Init, condition, increment, body];
You have a problem at the part of the condition. I'm sure you ment 
For[i = 1, i <= 16000, i++, Lattice[[Random[Integer, {1, 100}]]]++]
Otherwise i will be set to 16000 and the loop wil not be executed
it is better to use the Do loop in this case, that is
Lattice= Table[0, {n, 100}];
Do[Lattice[[Random[Integer, {1, 100}]]]++, {16000}].
This way you probably will avoide some of these errors in the future
On 6/15/05, mchangun at <mchangun at> wrote:
> 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
> above?
> Thanks in advanced.

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