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MathGroup Archive 1997

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Re: Collect, Coefficient, and non-integer exponents

  • To: mathgroup at smc.vnet.net
  • Subject: [mg8769] Re: [mg8733] Collect, Coefficient, and non-integer exponents
  • From: Olivier Gerard <jacquesg at pratique.fr>
  • Date: Thu, 25 Sep 1997 12:26:04 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Sergio,

In my posting to the newsgroup, I made a mistake in writing down
your example. Fortunately my code will works for the original one too.

Allan Hayes has proposed a solution which is quite elegant .
But it works only with 3.0 and not with my
2.2 (Macintosh). In the latter case it hangs forever with
your test example. It seems the problem in his code is
the use of Exponent which works differently in 2.2 and in 3.0
as shows this test:

Exponent[x^45+10 x^(7000/81)+ 5x^(1000.3),x]

which gives 1000.3 in 3.0 but 7000/81 with 2.2, ignoring
approximate exponents in the latter case. A solution to
work this around would perhaps be the use of Rationalize[] ?
Of course it works in 2.2 if you express the exponents as 12/100 /n
and not 0.12/n .

In slight contradiction to what I said, Coefficient seems
to work in very general cases (even on 2.2 Mma on a Mac)
although CoefficientList does not works with rationals
in 2.2 and 3.0 and would not accept any non polynomial input.
(If there is at least one rational exponents, it puts everything
in the 0 exponent place, whereas if there are approximate exponents
it treats correctly the integer exponents present ).
This was the motivation of my code which works the same way
with every Mma version I tested it.

If you prefer the presentation given by Allan routine, just
Transpose my routine's output.


Olivier Gerard.





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