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Re: simple pattern match question

• To: mathgroup at smc.vnet.net
• Subject: [mg91185] Re: simple pattern match question
• From: Steven Siew <stevensiew2 at gmail.com>
• Date: Fri, 8 Aug 2008 07:17:32 -0400 (EDT)
• References: <g7ed78$2po$1@smc.vnet.net>

You should use the query (?)

In[1]:= f[x_?NumberQ] := x ^ 2
In[2]:= f[3]
Out[2]= 9

In[3]:= f[3.3]
Out[3]= 10.89

In[4]:= f[r]
Out[4]= f[r]

This means function f only works on things that return True on the
NumberQ[expr_] function

Steven Siew

On Aug 7, 6:54 pm, congruentialumina... at yahoo.com wrote:
> Hello UG:
>
> I am trying to understand simple pattern rule evaulation. The
> following trivial examples baffles me:
>
> ---------------------------------------------------
> In[1]:= f[x_Number] := x ^ 2
> In[2]:= f[3]
> Out[2]= f[3]
>
> In[3]:= f[3.3]
> Out[3]= f[3.3]
>
> In[4]:= NumberQ[3.3]
> Out[4]= True
> --------------------------------------------------
> Why is it that f[3.3] does not evaluate??
>
> TIA.
>
> Regards..RogerW