Re: Series expansion question

• To: mathgroup at smc.vnet.net
• Subject: [mg122717] Re: Series expansion question
• From: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>
• Date: Mon, 7 Nov 2011 05:53:38 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

```Hi, Recif,

This:

Clear[gts];

gts[x_, y_] := Normal[Series[g[x, y], {x, x0, 1}, {y, y0, 1}]];

gts[x, y] /. {x -> x0 + z, y -> y0 + z}

may help. Try. Have fun.

I defined a function:

gts[x_, y_] := Normal[Series[g[x, y], {x, x0, 1}, {y, y0, 1}]]

and when I use it with 'a' and 'b' undefined, I get the value I expect:

gts[a, b]

g[x0,y0] + (a-x0) g^(1,0)[x0,y0] + (b-y0) g^(0,1)[x0,y0] ...

However when I assign values to a and b:

a = x0 + z

b = y0 + z

gts[a,b]

gives me an error:

General::ivar: "x0+z is not a valid variable"

etc.

I would appreciate any help to fix this.

Thanks.

Recif

Alexei BOULBITCH, Dr., habil.

IEE S.A.

ZAE Weiergewan,

11, rue Edmond Reuter,

L-5326 Contern, LUXEMBOURG

Office phone :  +352-2454-2566

Office fax:       +352-2454-3566

mobile phone:  +49 151 52 40 66 44

e-mail: alexei.boulbitch at iee.lu<mailto:alexei.boulbitch at iee.lu>

```

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