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MathGroup Archive 2005

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Re: Getting crude approximation to a function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58845] Re: Getting crude approximation to a function
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 21 Jul 2005 03:07:53 -0400 (EDT)
  • References: <dbkkpu$s6a$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Mukhtar,
with version:
5.1 for Microsoft Windows (October 25, 2004)
your input produces a fully rationalized output:

-13/3 + (2*x)/3 + (71*p*x)/100

sincerely, Daniel

Mukhtar Bekkali wrote:
> Assume I have a function f[x], x is some variable, given below (my real
> function is much more complex). I would like to obtain its crude
> approximation. I used command Series, first order expansion. The
> resulting function has coefficients that have high precision. I do not
> need that since my expansion is very crude anyway. I need coefficients
> that are rational number approximations to these coefficients. How do I
> obtain this? It seems to me that command Chop takes care of
> coefficients that are not product with variable x but cannot handle
> coefficients that are not standalone. For instance, in this example
> 
> \!\(\(\(Normal[
>         Series[0.71  p\
>             x + \(1\/3\)
>             x\^2 - 4, {x, 1, 1}]] // Expand\) // Chop\) //
> Rationalize\)
> 
> I would like to obtain output of the form (-13/10)+(29/10)x.
> Mathematica gives me (-13/10)+2.8972x instead, where it keeps
> 2.8971974507154195` in the memory. I need this because I use
> InequalitySolve package and it refuses to function unless all numbers
> are rational.  
> 
> Mukhtar Bekkali
> 




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