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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


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