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Re: Turning Derivative into Function (Newbie Question)

• To: mathgroup at smc.vnet.net
• Subject: [mg115481] Re: Turning Derivative into Function (Newbie Question)
• From: dsnead6 at charter.net
• Date: Wed, 12 Jan 2011 04:07:02 -0500 (EST)

Define g as
g[x_]:=f'[x]


--Dave


On Tue, Jan 11, 2011 at 3:58 AM, 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 :)