Re: Defining derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg87959] Re: Defining derivatives
- From: dh <dh at metrohm.ch>
- Date: Mon, 21 Apr 2008 03:26:23 -0400 (EDT)
- References: <fu9vnl$igu$1@smc.vnet.net>
Hi, thank's a lot for the replies. Here is a short summary of what I just learned: - expressions with the form: f[..][..] are called SubValues of f. Documentation of this is non existent, but mathematica knows about it. - the best way to define derivatives is: Derivative[1][f]= f2 however, what is still not clear to me is why the following does not work: Derivative[1][f][x_]= f2[x] thank's again, Daniel dh wrote: > Hello All, > > does anybody know how to define symbolic derivatives. E.g.: > > f[x_]:=f1[x]; > > f'[x_]:=f2[x]; > > this does not work because f on the lefthand side is evaluated. To > > prevent this (do not forget to remove f before redefining it): > > f[x_]:=f1[x]; > > HoldPattern[f'[x_]]:=f2[x]; > > this gives no message, but f'[x] returns f1[x] instead of f2[x]. > > The same thinhg happens when you change the sequence of definitions: > > f'[x_]:=f2[x]; > > f[x_]:=f1[x]; > > Further, where is the information about derivatives stored? > > thank's a lot, Daniel > > >