Re: Turning Derivative into Function (Newbie Question)

*To*: mathgroup at smc.vnet.net*Subject*: [mg115468] Re: Turning Derivative into Function (Newbie Question)*From*: Peter Pein <petsie at dordos.net>*Date*: Tue, 11 Jan 2011 19:23:18 -0500 (EST)*References*: <ighgml$al6$1@smc.vnet.net>

On 11.01.2011 12:59, Just A Stranger wrote: > When I apply a function that outputs another function, how come I can not > pass arguments to the new function? Am I missing some principle about how > Mathematica functions work? Could someone please point me to the relevant > documentation? > > > A simple example to illustrate my confusion: > > In[1]: f[x_] := x^2 > In[2]: g := f'[x] > > So now I have: > > In[3]: g > out[3]: 2x > > as expected > > So how come I get the following when trying to pass an argument to g: > > In[4]: g[2] > Out[4]: 2x[2] > > Instead of the output I want: > > *Ou[4]: 4 > > > I tried > > In: g[x_] := f'[x] > > But it seems to think I'm trying to assign a function to Times. > "SetDelayed::write: Tag Times in (2 x)[y_] is Protected.>>" > > Thank you very much for any help :) > > Hi stranger, I guess, you tried g[x_]:=f'[x] while g hold still 2*x. Try Clean[g] before assigning a new value. I would use f[x_] := x^2; g = Derivative[1][f]; g[z] --> 2 z Peter