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Series expansion question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122696] Series expansion question
  • From: Recif <recif at yahoo.com>
  • Date: Sun, 6 Nov 2011 05:56:39 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

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



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