Re: Series expansion question
- To: mathgroup at smc.vnet.net
- Subject: [mg122707] Re: Series expansion question
- From: "Dr. Wolfgang Hintze" <weh at snafu.de>
- Date: Mon, 7 Nov 2011 05:51:50 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <j95pf3$m7v$1@smc.vnet.net>
"Recif" <recif at yahoo.com> schrieb im Newsbeitrag news:j95pf3$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