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Re: Getting crude approximation to a function

  • To: mathgroup at
  • Subject: [mg58849] Re: [mg58832] Getting crude approximation to a function
  • From: yehuda ben-shimol <bsyehuda at>
  • Date: Thu, 21 Jul 2005 03:07:55 -0400 (EDT)
  • References: <>
  • Reply-to: yehuda ben-shimol <bsyehuda at>
  • Sender: owner-wri-mathgroup at

Hi Mukhtar,
If you use rational and integers only for the coefficients you will
not need Chop and Rationalize. It will return an expression with
rationals and integers only

On 7/20/05, Mukhtar Bekkali <mbekkali at> 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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