Re: How to extract functions from a list and call them with any argument?

• To: mathgroup at smc.vnet.net
• Subject: [mg65957] Re: How to extract functions from a list and call them with any argument?
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Mon, 24 Apr 2006 06:02:19 -0400 (EDT)
• References: <e2fkto\$bp7\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

dmp55 at sympatico.ca wrote:
> I have a list of functions, i.e.,
>
> funclist = {Sin[x], x^3, Cos[x]^2}.
>
> I can extract each of the functions, like
>
> In[1]:=funclist[[1]]
> Out[1]=Sin[x]
>
> , but I don't know how to call these functions with a general argument.
> If I type
>
> In[2]:=funclist[t][[1]]
>
> , I get
>
> Out[2]=t
>
> instead of Sin[t] (or t^3 or Cos[t]^2)
>
> What I would like is to extract a function from the list and to call it
> with any argument, as it was defined in a standard way:
> f[x_]:=Sin[x].
>
> Dom
>
The short answer is that you don't have a list of functions - you have a
list of expressions, so you need to replace x by whatever you want:

funclist[[1]]/. x->t

However, this is not an ideal way to work because if x gets a value
somewhere else, that value will get substituted before you can get the
desired replacement. It would probably be better to use a real list of
functions - pure functions - looking like:

{Sin,#^3&,Cos[#]^2&}

Your question indicates that you are probably a beginner with
Mathematica, and it would really help to read that big book a bit and
try the examples. After a while, you will find that the right way to do