RE: newbie question: generic derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg41581] RE: [mg41563] newbie question: generic derivatives
- From: "Florian Jaccard" <jaccardf at eicn.ch>
- Date: Tue, 27 May 2003 05:25:30 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
you want : df/dx = pf/py y' + pf/py' y''= Dot[grad[f[y,y']],{y',y''}]
You can create what you want !
The function grad :
grad[f_, vars_List] := (D[f, #] & /@ vars)
Then the function wich calculates the total derivative :
derTot[f_, vars_List, indepVar_] := grad[f, vars].(D[#, indepVar] & /@ vars)
You can know try it on your example :
derTot[f[y[x], y'[x]], {y[x], y'[x]}, x]
And you will see that it works fine !
Meilleures salutations
Florian Jaccard
-----Message d'origine-----
De : Eduardo Suárez [mailto:bardino at mail.com]
Envoyé : mar., 27. mai 2003 07:47
À : mathgroup at smc.vnet.net
Objet : [mg41563] newbie question: generic derivatives
Hello all.
I'm new to mathematica and i'm trying to do some partial derivatives.
I have y(x) and f(y,y') and would like to get:
df/dx=...
Is there a way to get a result without defining 'f' and 'y'. I mean
df/dx = pf/py y' + pf/py' y''.
Thanks in advance,
-Eduardo