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MathGroup Archive 1997

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Re: Q: Collect, Coefficient, and non-integer exponents [2]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg8766] Re: [mg8733] Q: Collect, Coefficient, and non-integer exponents [2]
  • From: Allan Hayes <hay at haystack.demon.co.uk>
  • Date: Sun, 21 Sep 1997 20:51:09 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Sergio,
Here is  a  development based on Coefficient working for inexact  
exponents.

unZip[expr_] :=
  Rest[Thread[Rest[
  	FixedPointList[
  		{Expand[#1 - #2*x^#3], #2, x^#3} & [
  		#1, Coefficient[#1, x^#2], #2] & [
  		#1[[1]], Exponent[#1[[1]], x]] & ,
  		{expr, 0, 0},
      	SameTest -> (#2[[1]] === 0 &)
     ]
   ]]]

expr = Expand[Sum[(a*n +b*n -c)*x^(n+0.12/n),{n,1,4}]];

unZip[expr]
	
	{{4a + 4b - c, 3a + 3b - c, 2a + 2b - c, a + b - c},
  	 {x^4.03, x^3.04, x^2.06, x^1.12}
	}

Check:

Dot@@%
	(a + b - c) x^1.12 + (2a + 2b - c) x^2.06 +
  	   (3a + 3b - c) x^3.04 + (4a + 4b - c)x^4.03

expr-%//Expand
0

Allan

Allan Hayes
hay at haystack.demon.co.uk
http://www.haystack.demon.co.uk/training.html
voice:+44 (0)116 2714198
fax: +44 (0)116 2718642
Leicester,  UK


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