Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1997
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1997

[Date Index] [Thread Index] [Author Index]

Search the Archive

Exponent function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7807] Exponent function
  • From: Raya Firsov-Khanin <raya at mech.ed.ac.uk>
  • Date: Sat, 12 Jul 1997 02:45:49 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hello, 

I've noticed the following strange feature of 

Exponent[expr, arg, List]

function of Mathematica.  Suppose I want to 
find all powers of x in the expression of the type 

test = x + x^(1+a) + x^(-1+a) + x^2 

then Exponent[test, x, List] gives the correct result 

{1, 2, 1-a, -1+a}. 


Suppose now, I add x^(-1) to test:  

test1 = test + x^(-1) 

then 

Exponent[test1, x, List] gives a result {-1, -1, 1, 1, 2}. 

For expressions like 

test2 = test + x^(-n) the result of Exponent[] is correct 

{1, 2, 1-a, -1+a, -n}, while for expressions where n is specified, 
e.g.  n=1, 2, 3, ...  the result is always wrong.

I need to use Exponent function in a program that
should solve nonlinear problems using Multiple Scale Method. I need to
identify exponential frequencies of different terms in the equations, and
to study under what conditions they become resonant.  

Any suggestions on how I can make Exponent function to give correct 
results? Or may be there are some other ways to find powers of x in the 
expressions of the type written above.  
Any help would be appreciated. I already spent a morning trying to solve 
this puzzle.  
		Thanks a lot. 
                		 Raya


  • Prev by Date: Re: graphics import/conversion bug?
  • Next by Date: Re: character problem
  • Previous by thread: Question regarding expressions with Sum[...]
  • Next by thread: Re: character problem