MathGroup Archive 1999

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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 
  
 



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