RE: Differentiating functions of vectors
- To: mathgroup at smc.vnet.net
- Subject: [mg9449] RE: [mg9424] Differentiating functions of vectors
- From: jmthomas <jmthomas at cybercable.tm.fr>
- Date: Thu, 6 Nov 1997 02:39:58 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Your function is f[ a_ , b_ ] := a . b but I need to know the kind of data structure that a and b refer to: are = they vectors (like the dot suggests)? If it is the case, differentiating = with respect to a certain argument implies in fact tensor analysis, = which is not present as a standard routine set in mathematica. See = MathTensor, references are given to it in wolfram Research site. If a and b are just reals or complexes, you can use: op1=Derivative[1,0][#]& op2=Derivative[0,1][#]& If f[a_,b_]=2a+b you will get op1[f]=2& and op2[f]=1& ----------------------------------------------- Jean-Marie THOMAS Conseil et Audit en Ing=E9nierie de Calcul jmthomas at cybercable.tm.fr www.cybercable.tm.fr/~jmthomas -----Original Message----- From: Loris Bennett [SMTP:loris at ferro.physik.TU-Berlin.DE] To: mathgroup at smc.vnet.net Sent: Wednesday, November 05, 1997 7:57 AM To: mathgroup at smc.vnet.net Subject: [mg9424] Differentiating functions of vectors --------------E197FA4B98680772E12058D3 Hello, If I have a function such as f[ a_ , b_ ] := a . b how do I differentitate w.r.t a certain component without having to specify the components of the vector explicitly? I had hoped something like fa[ a_ , b_ ] = D[ f [ a . b ] , a[[1]]] would work, but it doesn't.. All help greatly appreciated. Loris