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MathGroup Archive 2000

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Re: Getting coordinates of array member

  • To: mathgroup at smc.vnet.net
  • Subject: [mg26263] Re: Getting coordinates of array member
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sun, 10 Dec 2000 00:19:37 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <90krir$r50@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

that looks not mich like a Mathematica question ?
You may look at "The Art of Computer Programming" Volume I
that contains an extensive chapter on linear addressing.

You have a (n,m) array and 

(i,j)=(1,3)   

the linear index is k=j*n+i  

The reversion is done by

j=Mod[k,n] 
i= k-j*n


Regards
  Jens

PS: Is it right that you transpose the index because 7 is on
position (3,1) in your matrix?

Stephane Hebert wrote:
> 
> Hi folks,
> 
> Ok, let's say I have this
> 
>      1  2  3
>     -----------
>  1| 1  2  3
>  2| 4  5  6
>  3| 7  8  9
> 
> A 3x3 matrice or array.  Each number in the array represents its' position
> from top left to bottom right.
> 
> What I need to do is:
> 
> Find what position 1,3 is.  Just by looking at the array, we find that 7 is
> the answer.
> 
> Find what are the coordinates of 7.  Again just by looking at the array we
> see that the answer is 1,3
> 
> I need to come up with a simplu function that will return these.
> 
> pos = GetPos(x,y)
> 
> coord = GetCoord(pos)
> 
> I've done this before, way long ago and can't find it.
> 
> Thanks.
> 
> --
> Stephane Hebert
> =========================
> stephhebert at yourpants~videotron.ca
> Remove yourpants~ to reply
> =========================


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