Re: D
- To: mathgroup at smc.vnet.net
- Subject: [mg94553] Re: D
- From: dh <dh at metrohm.com>
- Date: Tue, 16 Dec 2008 02:34:08 -0500 (EST)
- References: <ghtjb8$r6c$1@smc.vnet.net>
Hi Cetin,
try not to overload your question with insignificant details. The epsj
are unimportant for the derivatives, I do not write them. Further, I
give the principle for only 2 functions and variables, otherwise it will
be a mess to check if everything is correct.
We want the Jacobian of f1[y1,y2] and f2[y1,y2]. This is sort of an
outer product between fi and derivative in direction yj:
funs={f1,f2};
vars={y1,y2}
Outer[D[#1@@vars,#2]&,funs,vars]
For many dimensions it mqay be profitable to generalise this further. If
we denote the functions f1,.. by f[1],.. and the variables y1,.. by y[1]
we can write:
funs=Array[f,2];
vars=Array[y,2];
Outer[D[#1@@vars,#2]&,funs,vars]
For 21 dimensions, you simply have to reaplce 2 by 21.
hope thsi helps, Daniel
Cetin Haftaoglu wrote:
> Dear mathematica users,
>
>
>
> I have a to evaluate the Jacobian matrix from a vector of function fi,
> i=1,21 with the inner variables yi, i=1, 21 and epsj j=1,6.
>
> So I have to evaluate D[f_i [yi,epsj] , y_j], i= 1, 21, j=1, 21. How can I
> write this expression in a short form, without to say that the functions f_i
> depent on the inner
> variables yi. When I write D[f_i,yi] I receive 0 because mathematica thinks
> that I want derive a Constant. When I say
>
>
>
> D[f_i[y1,y2,y3,=85.,y21,eps1,=85eps6],y_j] ], i= 1, 21, j=1, 21
>
>
>
> I get the right expression but a very great expression (output). How can I
> reduce this output?
>
>
>
> TIA,
>
> Regards,
>
>
>
> Cetin Haftaoglu
>
> Arbeitsgruppe " Modellierung und Simulation in der Werkstoffmechanik"
>
> BAM =96 Bundesanstalt f=FCr Materialforschung und -pr=FCfung
> Fachgruppe V.2 =96Werkstoffmechanik
>
>
>
> Unter den Eichen 87
>
> D-12205 Berlin
>
> Deutschland
>
>
>
> Tel: +49-30-8104-3194
>
> Fax: +49-30-8104-1527
>
> Email: <mailto:cetin.haftaoglu at bam.de> cetin.haftaoglu at bam.de
>
> Web: www.bam.de