Re: Why does Derivative fail in this case?

*To*: mathgroup at smc.vnet.net*Subject*: [mg96583] Re: [mg96557] Why does Derivative fail in this case?*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Mon, 16 Feb 2009 16:40:14 -0500 (EST)*References*: <200902161158.GAA03553@smc.vnet.net>*Reply-to*: drmajorbob at longhorns.com

This works: f[x_, y_] := x y g = f[##]*f[##] &; h[x_, y_] := D[g[x, y], x] g[x, y] h[x, y] x^2 y^2 2 x y^2 As to why the other did not? Not sure. I do know it's often a poor idea to write functions without arguments. Bobby On Mon, 16 Feb 2009 05:58:26 -0600, Aaron Fude <aaronfude at gmail.com> wrote: > Hi, > > This example is self-explanatory: > > f[x_, y_] := x y > g = f[##]*f[##] &; > h = Derivative[1, 0][g]; > g[x, y] > h[x, y] > > I should expect that h[x, y] is 2 x y^2, but instead it is zero. How > come? > > Version 6.0 > > Many thanks in advance, > > Aaron > -- DrMajorBob at longhorns.com

**References**:**Why does Derivative fail in this case?***From:*Aaron Fude <aaronfude@gmail.com>