       Re: Tips for writing correct, non trivial Mathematica Libraries

• To: mathgroup at smc.vnet.net
• Subject: [mg124442] Re: Tips for writing correct, non trivial Mathematica Libraries
• From: "l.i.b." <nehal.alum at gmail.com>
• Date: Fri, 20 Jan 2012 01:46:51 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <jf8qj3\$3of\$1@smc.vnet.net>

```Thanks for your comments.  My followups are inlined below:

> >** Take for example the following: (Taken from the mathematica 8
> >virtual book section "Applying Functions to Lists and Other
> >Expressions")
> >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

the snippet for 'geom' is taken for the mathematica tutorial, and is
meant to show the user how to define a function that implements the
geometric mean.  so for instance,
geom[{x,y,z}] = (x y z )^(1/3).  But geom[x+y] treats the expression
as a list and returns Sqrt[x y], which is not what a new user would
expect ( a better answer would be x+y)

>
> >The built-in function GeometricMean properly complains when given
> >this input,
>

I'm saying GeometricMean does not get fooled by GeometricMean[x+y],
which means the author thought of how to protect it from doing the
wrong thing -- and it would be nice to see exactly what syntax they
used.

>
> If you want to look at examples of well written Mathematica
> packages, a good place to start is to look at the packages that
> ship with Mathematica.
Actually that's exactly what I've started to do, once I nailed down
the location of the bundled packages.  Though I've yet to find the
definition for GeometricMean in the install directory -- presumable it
is a native command.

Thanks

```

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