Re: Why does Derivative fail in this case?
- To: mathgroup at smc.vnet.net
- Subject: [mg96582] Re: Why does Derivative fail in this case?
- From: dh <dh at metrohm.com>
- Date: Mon, 16 Feb 2009 16:40:03 -0500 (EST)
- References: <email@example.com>
Hi Aaron, if you write: g = f[##]*f[##] &; the number of arguments to f is not defined until you execute g, specifying arguments. g alone will not evaluate. Therefore g is treated as a constant in: Derivative[1, 0][g1]. As a remedy, spezify the arguments in: g1 = f1[#1, #2]^2 &; and all is well. hope this helps, Daniel Aaron Fude 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 >