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Re: Functions with optional parameters

• To: mathgroup at smc.vnet.net
• Subject: [mg51929] Re: Functions with optional parameters
• From: Curt Fischer <crf3 at po.cwru.edu>
• Date: Fri, 5 Nov 2004 02:17:34 -0500 (EST)
• References: <cmclfa$i7s$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Gregory Lypny wrote:
> Hello everyone,
> 
> How can I create functions with optional parameters?  For example, a 
> simple function to add two or three numbers:
> 
> addThem[a_,b_,c_]:=If[c is not empty, Sum[a,b,c],Sum[a,b]]
> 
> I'm not sure of the proper syntax to test whether c is null or empty.

Hi Greg,

Here is code I copied from the Mathematica 5.0.1 Help Browser, which I 
got from looking up BlankNullSequence (___).

In[1]:=
f[x_,y___]:=x+y

In[2]:=
f[a,b,c,d]

Out[2]=
a+b+c+d

In[3]:=
f[a]

Out[3]=
a

-- 
Curt Fischer