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MathGroup Archive 2005

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Re: Controlled evaluation of functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56800] Re: Controlled evaluation of functions
  • From: Peter Pein <petsie at dordos.net>
  • Date: Fri, 6 May 2005 03:00:19 -0400 (EDT)
  • References: <d5ct4c$m5c$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Brett Patterson wrote:
> Consider the following behaviour:
> 
>   In[1]:= f[i_, x_] := Sin[i x]
> 
>   In[2]:= g[x_] = Table[f[i, x], {i, 3}]
> 
>   Out[2]= {Sin[x], Sin[2 x], Sin[3 x]}
> 
>   In[3]:= {3, 0, 1} . g[y]
> 
>   Out[3]= 3 Sin[y] + Sin[3 y]
> 
> This is what I want to do, but using my own function instead of Sin.
> However, this is the result:
> 
>   In[4]:= k[x_] := x^2           (* This is my alternative to Sin *)
> 
>   In[5]:= f[i_, x_] := k[i x]
> 
>   In[6]:= g[x_] = Table[f[i, x], {i, 3}]
> 
>   Out[6]= {x^2, 4 x^2, 9 x^2}    (* I want {k[x], k[2 x], k[3 x]} *)
> 
>   In[7]:= {3, 0, 1} . g[y]
> 
>   Out[7]= 12 y^2                 (* I want 3 k[y] + k[3 y] *)
> 
> How can I get the function k to behave like Sin, so that it is not
> evaluated?
> 
> Note that in my real application, k is a lot more complex and has
> conditions on its arguments, etc.
> 
> Thanks!
> 
> Brett Patterson
> 
Hi,

there are at least 2 possibilities:

a) leave k undefined
b) k[x_?NumericQ]:=x^2 evaluate for numeric arguments only

-- 
Peter Pein
Berlin


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