Re: Why does Derivative fail in this case?
- To: mathgroup at smc.vnet.net
- Subject: [mg96607] Re: Why does Derivative fail in this case?
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Tue, 17 Feb 2009 06:25:14 -0500 (EST)
On 2/16/09 at 6:58 AM, aaronfude at gmail.com (Aaron Fude) wrote: >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? Because g is not a function of either x or y. You have defined g to be a pure function. Doing g[x,y] does not change the definition of g. So, for the definition of h, Derivatitive[1, 0][g] is evaluated to 0& and this result is assigned to h. Consequently, any argument supplied to h will return 0. You can easily verify the value assigned to h by doing OwnValues[h]