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Re: Basic questions on _Plus and recursion

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  • Subject: [mg120885] Re: Basic questions on _Plus and recursion
  • From: Heike Gramberg <heike.gramberg at>
  • Date: Sun, 14 Aug 2011 08:14:35 -0400 (EDT)
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  • References: <>

You could try Distribute:



f[a, c] + f[a, d] + f[b, c] + f[b, d]


On 13 Aug 2011, at 12:49, Ethan Dyer wrote:

> Hi. I'm sure these are common issues, but I haven't found them. Here 
are the two, unrelated questions. Thank you for the help.
> 1) I want to use _Plus for a function with arbitrary arguments. ie I 
want: f[a+b]=f[a]+f[b], f[a+b,c+d] to go to =
f[a,c]+f[a,d]+f[b,c]+f[b,d], ... Is there a standard way to do this?
> 2)Here I want to pull out scalars from a function. Something like 
> f[x__] :=(Times@@Select[{x},Scalar[#]==1&]) =
> Where i have defined a function Scalar to =1 for some symbols.
> for instance say I had defined Scalar[a]=1 then f[a,b,c]= a 
> The above does not work, as it gives infinite recursion. Is there a 
way to do this properly?
> Thank you again. Sorry if these are too common.
> Ethan

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