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Re: Dont Understand

  • To: mathgroup at
  • Subject: [mg15903] Re: Dont Understand
  • From: Martin Kraus <mkraus at>
  • Date: Wed, 17 Feb 1999 23:33:45 -0500
  • Organization: Regionales Rechenzentrum Erlangen, Germany
  • References: <7a2bm8$>
  • Sender: owner-wri-mathgroup at

Don McKenzie Paul wrote:
> I'm not an expert in Mathematica and would appreciate comments on why
> init1 returns a list with all zeros replaced by -1, but init does not.
> Its probably very simple but its confused me.
> Don
> init[n_Integer]:=Module[
>                     {s=Table[Random[Integer],{n n}]},
>                     s/.{0->-1};
>                     Partition[s,n]
>                     ]
> init1[n_Integer]:=Module[
>                     {s=Table[Random[Integer],{n n}]},
>                     s/.{0->-1}
>                     ]
> --
> Prof. Don McKenzie Paul               tel.  (1203) 523603 Department of
> Physics                 fax.  (1203) 692016 University of Warwick
> email  phrje at COVENTRY CV4 7AL
> UK

I think you just forgot to set s to its new value in init:
s=s/.{0->-1} (instead of s/.{0->-1}), because if you do not set s, 
the replacement will have no effect in init. 
On the other hand in init1 the new value of s is returned as 
this is the last instruction in this module; thus, there is no
need to set s to this value in this case.

Hope that helps

Martin Kraus

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