       Re: infuriating Series[] question

• To: mathgroup at smc.vnet.net
• Subject: [mg17257] Re: infuriating Series[] question
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 30 Apr 1999 02:34:43 -0400
• Organization: Universitaet Leipzig
• References: <7g0spa\$dvc@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi Peter,

be a bit more clear what do you expect from Simplify[] and
FullSimplify[].
That what you get from Series[] is *not* what you see !
You see a funny

a+b*x+c*x^2+O[x]^3

that looks like a sum with a strange O[x]^3 term. But Mathematica has
saved it as

SeriesData[x,0,List[a,b,c],0,3,1]

that means it is a series in x at x=0 with coefficients {a,b,c} with
minimal
exponet 0, maximal exponent 3 and the common denominator of the exponent
1.

You can use Normal[] to convert the series to a polynom and some
functions
like NumericalMath`Horner`Horner[] will now work. You may also
Simplify[]
the coefficients of the series by

ser[]=(Simplify /@ #) &[ser[]]

but to give you a better advice I must know "what did you expect?"

Regards
Jens

Peter Jay Salzman wrote:
>
> Dear all,
>
> I'm trying to develop very high order difference equations, and want to use
> Mathematica to save me from calculating tons of quantities like 5^10 / 7!
>
> If I define:
>    g[x_] := Series[ f[x], {x,0,10} ]
>
> And try to compute stuff like:
>
>    g[5*h] or g[10*h]
>
> It gives me the right answer, but i get terms like
>
>    f''''' * (5 x)^(10) / 10!
>
> The whole point in using Mathematica is so that I don't have to calculate things
> which look like 5^10 / 10!   (that's factorial, of course, not me being
> emphatic).
>
> Even when I try things like // Simplify or // FullSimplify, Mathematica refuses to
> simplify these rational coefficients.   One thing I've learned is that Mathematica
> can do anything -- but figuring out how to do the something is often
> completely not obvious to a nominal user like me.
>
> Can someone tell me the secret here?
>
> Pete
>

```

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