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Re: remove higher orders terms from mathemtica's result

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90928] Re: remove higher orders terms from mathemtica's result
  • From: Alois Steindl <Alois.Steindl at tuwien.ac.at>
  • Date: Wed, 30 Jul 2008 03:51:50 -0400 (EDT)
  • Organization: Inst. f. Mechanics II, TU Vienna
  • References: <g6mqap$nt8$1@smc.vnet.net>

kem <kemelmi at gmail.com> writes:

> Hi,
> Given this:
>
> K = (1+vy) (zx+wx)  + vx (zy+wy);
> Expand[K^2]
>
> Is it possible to remove automatically the 3rd and 4th orders from the
> result of  'Expand[K^2]' ?
>
> By 3rd order I mean terms like: 2 wy zy vx^2  etc. (all terms with sum
> of the degrees of derivatives of u,v,w is = 3)
> By 4th order:  wy^2 vx^2  etc.   (sum of degrees of u,v,w = 4)
>
>
> Thanks
Hello,
isn't 2 wy zy vx^2 a 4th order term? (I admit, that I don't understand
your quatities sufficiently well. What is zy?)

You could multiply all variables with a weighting factor
epsilon, calculate a Series in epsilon, Normalize, and set
epsilon=1. This also helps, if you need other weighting factors
(eg. consider w itself as 2nd order).

Good luck
Alois



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