Re: partial derivate of a function of vector variable
- To: mathgroup at smc.vnet.net
- Subject: [mg108635] Re: partial derivate of a function of vector variable
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Thu, 25 Mar 2010 06:08:46 -0500 (EST)
- Reply-to: hanlonr at cox.net
f[x_] := x.x
x = {x1, x2, x3};
f[x]
x1^2 + x2^2 + x3^2
D[f[x], #] & /@ x
{2 x1,2 x2,2 x3}
D[f[x], x[[1]]]
2 x1
Bob Hanlon
---- atlas shrugger <ashrugger at gmail.com> wrote:
=============
Hi,
Let's say have function f of vector variable x.
f[x_] := x[[1]]^2 + x[[2]]^2
How to compute partial derivate by x_1?
Something like D[f[x], {{x[[1]]}}] does not work.
I don't want to rewrite function f as f[x1_,x2_].
Thanks for help.