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Re: Default and head in function argument

• To: mathgroup at smc.vnet.net
• Subject: [mg111643] Re: Default and head in function argument
• From: "Scot T. Martin" <smartin at seas.harvard.edu>
• Date: Sun, 8 Aug 2010 07:23:31 -0400 (EDT)

I believe that you're after:

f[x:_Integer?(Positive):3] := x^3

The important point is the use of "(...)" to keep Mathematica oriented 
about your intentions.


On Sat, 7 Aug 2010, NP wrote:

> Hi,
>
> I know how to define a function so that it evaluates only when the
> head of the argument is of a certain type:
>
> Clear[f];
> f[x_Integer?Positive] := x^3
> f[3]
> f[3.1]
> f[-3]
>
> 27
> f[3.1]
> f[-3]
>
> and I also know how to set default to an argument of a function like
> so:
>
> Clear[f]
> f[x_:3]
> f[]
>
> 27
>
> How do I do both i.e., specify head and default value?
>
> Thanks,
>
> NP
>
>