Re: simple Problem: D[ ]

*To*: mathgroup at smc.vnet.net*Subject*: [mg27331] Re: simple Problem: D[ ]*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Wed, 21 Feb 2001 03:17:06 -0500 (EST)*References*: <96t91a$pqt@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Christian, It works OK for me f[x]=x^2 x^2 abl=D[f[x],x] 2 x But all that happens here is that D[f[x],x] changes to D[x^2,x] and then to 2x. We are actually differentiation an expression in x, not a function. The function approach is g[x_]:= x^2 g'[x] 2 x g'[5] 10 But beware, D[g[a],x] 0 since g[a] is a^2 with no x in it. -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Christian Maier" <maier1 at sbox.tu-graz.ac.at> wrote in message news:96t91a$pqt at smc.vnet.net... > > I use mathmatica the first time and have a problem with a deriviation: > > in a simple problem: > > f[x]=x^2 > abl=D[f[x],x] > > then Mathematica puts out f[x]' , but not 2 x > > How does it work correctly? > Thank aou in advance! > > Christian Maier > > >