       Re: Tips for writing correct, non trivial Mathematica Libraries

• To: mathgroup at smc.vnet.net
• Subject: [mg124441] Re: Tips for writing correct, non trivial Mathematica Libraries
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Fri, 20 Jan 2012 01:46:29 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201201191012.FAA03722@smc.vnet.net>

```On 19 Jan 2012, at 11:12, Bill Rowe wrote:

>>
>> geom[list_] := Apply[Times, list]^(1/Length[list])
>
>> So, this does a bad thing for geom[ x+ y]  (returns (Sqrt[x y])
>
> What were you expecting here? This looks correct to me

Clearly he sees what actually is a powerful feature of Mathematica as a
"bad thing". The feature is that a function whose arguments are not
restricted by pattern maching can be put to a more general use. I think
it's great and not "bad". If you want to restrict the function to work
on lists you can do this:

geom[list_List] := Apply[Times, list]^(1/Length[list])

and now

geom[list_List] := Apply[Times, list]^(1/Length[list])

geom[x + y]

geom[x + y]

and if you really wish you can restrict it only to vectors you can do

geom[list_?VectorQ] := Apply[Times, list]^(1/Length[list])

and so on.

This is much more powerful and flexible than the "other" approach.

Andrzej Kozlowski

```

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