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MathGroup Archive 2002

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RE: Re: Q: Simplify with "much less" assumptions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35657] RE: [mg35622] Re: [mg35600] Q: Simplify with "much less" assumptions
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Wed, 24 Jul 2002 02:06:41 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

When you say, "x is much less than y", do you mean close to 0?  Or close
to -Infinity?  In either case, there's no good definition of "simplify"
unless you mean to take the Limit, and that only works if the function
has a limit at 0 or -Infinity.  You can use Limit or you can simply
substitute x->0.

Be clear on what you want, and I think the solution will become obvious.

Bobby

-----Original Message-----
From: Xuguang(Heather) Zhang [mailto:xuguang_zhang at hotmail.com] 
To: mathgroup at smc.vnet.net
Subject: [mg35657] [mg35622] Re: [mg35600] Q: Simplify with "much less"
assumptions


AW: [mg35600] Q: Simplify with "much less" assumptionsThank you, bode. 
Maybe the last example I gave is too simplified. In fact, the problem I 
always meet with is as follows:
F(x,y,w,z) is a function of x,y,w and z where x,y,w and z are greater 
than zero. I want to simplify F(x,y,w,z) under the assumption that x is 
much less than y.
Can you please tell me how to do that? Thank you.

----- Original Message -----
  From: Matthias.Bode at oppenheim.de
To: mathgroup at smc.vnet.net
  Sent: Monday, July 22, 2002 8:48 AM
  Subject: [mg35657] [mg35622] AW: [mg35600] Q: Simplify with "much less"
assumptions


  Hello Heather,

  try:

  1 + x^2 /. {x -> 0}

  It will give you the 1 you wish.

  Best regards,
  Matthias Bode.

  Von: Xuguang(Heather) Zhang [mailto:xuguang_zhang at hotmail.com]
  Gesendet: Montag, 22. Juli 2002 08:11
  An: mathgroup at smc.vnet.net
  Betreff: [mg35600] Q: Simplify with "much less" assumptions




  Hello, everybody,

  I have one question regarding simplify answer with assumptions. For
  example, I have "1+x^2". The assumptions is  x is much much less than 
1.
  Therefore x^2 can be neglected under the above assumption. What I get
  after simplification should be "1" only. Can anybody tell me how do 
this
  in Mathematica? It seems there is no "much less" or "much greater"
  symbol in Mathematica. Thank you all.

  Heather





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