       Re: Getting crude approximation to a function

• To: mathgroup at smc.vnet.net
• Subject: [mg58849] Re: [mg58832] Getting crude approximation to a function
• From: yehuda ben-shimol <bsyehuda at gmail.com>
• Date: Thu, 21 Jul 2005 03:07:55 -0400 (EDT)
• References: <200507200429.AAA28544@smc.vnet.net>
• Reply-to: yehuda ben-shimol <bsyehuda at gmail.com>
• Sender: owner-wri-mathgroup at wolfram.com

```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
yehuda

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