re: Select peculiarity
- To: mathgroup at smc.vnet.net
- Subject: [mg16385] re: Select peculiarity
- From: Jack Goldberg <jackgold at math.lsa.umich.edu>
- Date: Thu, 11 Mar 1999 02:16:52 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Hi Group,
No sooner than I sent off my request for help on
explaining why Select[ g[x]*h[x], PolynomialQ[#,x]& ] returns 1
that I found the answer. Here it is.
It turns out that Times[] returns 1. I didn't know that!
So, when PolynomialQ finds no polynomials in g[x] or h[x] it
returns Times[] not Times[{}]. (The latter returns {}.) Likewise,
Select[ g[x]+h[x], PolynomialQ[#,x]& ] returns 0 since, it turns
out, Plus[] returns 0.
How about that!
Sorry to bother you all.
Jack