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Re: Positions of Polynomials in expr?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109368] Re: Positions of Polynomials in expr?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 23 Apr 2010 03:50:39 -0400 (EDT)

Any condition can be made a pattern

expr = {E^x, x, x^2, Log[x]};

Position[expr, _?(! PolynomialQ[#, x] &), 1]

{{1}, {4}}


Bob Hanlon

---- Jack L Goldberg 1 <jackgold at umich.edu> wrote: 

=============
Hi Folks,

"Select" and "Cases" are commands that do essentially the same thing,  
namely, pick out elements of a list which, in the first case matches a  
criterion, in the second case, matches a pattern.  I call these  
parallel commands.  Is there a command parallel to "Position" which  
uses criterion rather than pattern matching?

If no such parallel function exists, can one easily construct one?

I actually have a special case in mind.  I want to find the position  
of all parts of expr which fail the test PolynomialQ[f_,x].  Naively,  
I thought one might Map
Polynomial[#,x]& to all levels of expr and then find the positions of "False".
I haven't tried it because I'm betting someone knows how to do this  
neatly and I do not like to re-invent the wheel.  When I do so, the  
wheel tends to be more like an oval than a circle.

Thanks!

Jack



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