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MathGroup Archive 2001

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Re: Re: Special Matrix

  • To: mathgroup at
  • Subject: [mg28276] Re: [mg28231] Re: Special Matrix
  • From: Mianlai Zhou <lailai at>
  • Date: Sat, 7 Apr 2001 03:44:34 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

On Fri, 6 Apr 2001, Paul Lutus wrote:

> "Yoram Pollack" <syftech at> wrote in message
> news:9ah5nq$ps0 at
> > Hello
> > I am trying to create a "n x n" matrix with "1" in every position exept in
> > first and last row, and first and last coulumn, where "0" is needed. In
> > other words: sqare matrix full of  "1" sorounded by "0".
> > What will be the fastest and shortest way to do it?
> f[n_]:= Table[Sign[Mod[x*y,n-1]],{x,0,n-1},{y,0,n-1}]

This is wrong. When n is equal to 5, it will give a matrix with a 0 in the
coordinate of (3, 3), because that Mod[2*2, 5-1] == 0.

Should be corrected as:

Table[ Sign[Mod[x,n-1]*Mod[y,n-1]], {x,0,n-1}, {y,0,n-1} ]

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