MathGroup Archive 2011

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Series expansion question


"Recif" <recif at yahoo.com> schrieb im Newsbeitrag 
news:j95pf3$m7v$1 at smc.vnet.net...
>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
>

You should use replacements instead of assignments:

gts[a, b] /. {a -> x0 + z, b -> y0 + z}
Out[88]=
g[x0, y0] + z*Derivative[1, 0][g][x0, y0] +
z*(Derivative[0, 1][g][x0, y0] +
z*Derivative[1, 1][g][x0, y0])

Wolfgang 




  • Prev by Date: Re: Series expansion question
  • Next by Date: Scoping of pattern names
  • Previous by thread: Re: Series expansion question
  • Next by thread: Re: Series expansion question