Re: Re: Special Matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg28276] Re: [mg28231] Re: Special Matrix
- From: Mianlai Zhou <lailai at carmen.nikhef.nl>
- Date: Sat, 7 Apr 2001 03:44:34 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On Fri, 6 Apr 2001, Paul Lutus wrote: > "Yoram Pollack" <syftech at saad.org.il> wrote in message > news:9ah5nq$ps0 at smc.vnet.net... > > 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}] > Hi: 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} ]