RE: checking for a particular value in a matrix
- To: mathgroup at smc.vnet.net
- Subject: [mg30961] RE: [mg30933] checking for a particular value in a matrix
- From: "David Park" <djmp at earthlink.net>
- Date: Fri, 28 Sep 2001 03:55:11 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
This code will check that there is exactly one entry in a matrix of value 1. ExactlyOneOne[(mat_)?MatrixQ] := Count[mat, 1, Infinity] == 1 testmat1 = {{1, 0}, {2, 3}}; testmat2 = {{1, 0}, {2, 1}}; testmat3 = {{-1, 0}, {2, 3}}; ExactlyOneOne /@ {testmat1, testmat2, testmat3} {True, False, False} As for your second question, use a DelayedSet (:=). When you use Set (=) Mathematica calculates the right hand side of the definition immediately - even though the symbol a appears on the left hand side. This is a confusing aspect of Mathematica definitions that trips up many users. I don't know why Mathematica can't check to see if the symbol appears on the lhs. There is probably some logic to it. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ > From: Au Han Bin [mailto:auhb3 at cz3.nus.edu.sg] To: mathgroup at smc.vnet.net > > Hi, I am a programming newbie and I need advice on how to check that a > table or matrix , for all nonzero entries in a given row, has only one > entry of value 1. > > > > i have another query on why the code below does not work, when i call > convert{1,0,0,0} again, the results given are from an earlier question, > e.g. {1,1} is it initialised wrongly? > > > Clear[a,convert]; > convert[a___] = Sum[a[[i]]*2^(Length[a]-i),{i,1,Length[a]}] > > regards, thanks, > > joshua > >