Re: simple Problem: D[ ]

*To*: mathgroup at smc.vnet.net*Subject*: [mg27340] Re: [mg27310] simple Problem: D[ ]*From*: Jacqueline Zizi <jazi at club-internet.fr>*Date*: Wed, 21 Feb 2001 03:17:21 -0500 (EST)*References*: <200102200805.DAA26374@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

With my release (4.0) I get 2x, but of course if I ask for f[3] I get f[3] and not what expected (9). One solution is to define f in this way: f[x_] := x^2 If you are a mathematician, just think that x_ design a mathematical variable that can be replaced by what you want. If you are a computer man, then think that x_ is a filter of name x. In other cases, remember that in Mathematica, if you want a symbol to be replaced by something sometimes later, always use x_ or else think that you will have to operate on x substitutions using rules like x-> something. Jacqueline Zizi Christian Maier wrote: > 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

**References**:**simple Problem: D[ ]***From:*Christian Maier <maier1@sbox.tu-graz.ac.at>