Re: Conditional evaluations of functions
- To: mathgroup at smc.vnet.net
- Subject: [mg96514] Re: Conditional evaluations of functions
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sun, 15 Feb 2009 03:21:34 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <gn5udh$gsv$1@smc.vnet.net>
In article <gn5udh$gsv$1 at smc.vnet.net>, Asim <maa48 at columbia.edu>
wrote:
> I am not sure why the function g does not work, but the function f
> works as expected on Mathematica 7.0 on Windows XP. I want to get the
> sum of a vector only if the argument supplied is a numeric vector.
>
> In[1]:= g[x_?VectorQ[ x, NumericQ]] := Total[x]
>
> In[2]:= g[{a, b , c}]
>
> Out[2]= g[{a, b, c}]
>
> In[3]:= g[{1, 2, 3}]
>
> Out[3]= g[{1, 2, 3}]
[snip]
The test function that follows the question mark operator '?' is
expected to be a pure function. A *pattern*, like the one used for the
function f after the condition operator '/;' (which expect a pattern) is
*not* a pure function. Try
In[1]:=
g[(x_)?(VectorQ[#1, NumericQ] & )] := Total[x]
g[{a, b, c}]
g[{1, 2, 3}]
Out[2]= g[{a, b, c}]
Out[3]= 6
Regards,
--Jean-Marc