Best way to determine # of entries in a list?
- To: mathgroup at smc.vnet.net
- Subject: [mg42004] Best way to determine # of entries in a list?
- From: a_cjones at hotmail.com (cdj)
- Date: Mon, 16 Jun 2003 03:57:24 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hi, Example problem: To streamline the input of systems of linear equations, i'm setting up a function that accepts simply a flat list as argument. The first nxn entries are the rows of the matrix, and the last n are the target point (= b). This gives the length of the argument list as n^2 + n. I'd like to have a little bit of input error/type checking in the function. For this example, given a list, I'd like to test whether or not there exists an n such that length(list) = n^2 + n. The quickest/easiest way I know how to do it for this example problem is to test for integer-hood on sqrt[4*length(list) + 1] (yes = good data type). Q1: Does anybody know of a quicker/better/more elegant way to perform this test? Q2: In general, suppose i want to test (the length of) my list against an arbitrary polynomial P(n). What's the best way to do this? thanks for any insights, cdj