Re: partial derivate of a function of vector variable
- To: mathgroup at smc.vnet.net
- Subject: [mg108633] Re: partial derivate of a function of vector variable
- From: dh <dh at metrohm.com>
- Date: Thu, 25 Mar 2010 06:08:24 -0500 (EST)
- References: <hofa0t$4fd$1@smc.vnet.net>
Hi,
f[x_]:=..
is a function of one argument (even if your scalar is a list) and not a
function of several variables. Therefore there are no partial derivatives.
The easiest soultion would be to define a function of several variables,
but you do not want to do this.
Another solution is to "create" a function of several variables on the
fly, e.g. using dummy variables like:
D[f[{x1,x2},x1]]/.{x1->first argument, x2->second argument}
or we may use a pure function like:
Derivative[1, 0][Evaluate@f[{#1, #2}] &]
or another simpler possibility:
Evaluate@D[f[{#1, #2}], #1]&
Daniel
On 25.03.2010 10:22, atlas shrugger 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.
>
--
Daniel Huber
Metrohm Ltd.
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