Re: Defining derivatives

*To*: mathgroup at smc.vnet.net*Subject*: [mg87890] Re: [mg87851] Defining derivatives*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sat, 19 Apr 2008 03:36:41 -0400 (EDT)*References*: <200804181111.HAA18885@smc.vnet.net>

You can store it with Derivative. Not that In[7]:= Attributes[Derivative] Out[7]= {NHoldAll, ReadProtected} does not include Protected. So: f[x_] := f1[x] Derivative /: Derivative[1][f] = f2 gives f'[x] f2[x] Of course this still leaves the problem that D[f[x], x] Derivative[1][f1][x] but, on the other hand, why are you trying to do this? Why not simply define: f[x_] := f1[x] Derivative[1][f1] = f2; In which case we get also D[f[x], x] f2(x) Andrzej Kozlowski On 18 Apr 2008, at 20:11, 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 > > >

**References**:**Defining derivatives***From:*dh <dh@metrohm.ch>