Re: List arguments to functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg45559] Re: [mg45537] List arguments to functions*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Wed, 14 Jan 2004 01:26:13 -0500 (EST)*References*: <200401130903.EAA10620@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 13 Jan 2004, at 09:03, Chris Rozell wrote: > I have basic experience with Mathematica, but this problem has stumped > me for the last day or so. Any help would be appreciated. > > I have a function that needs to take two lists as arguments, perform > operations on them, and then sum the resulting list. However, by > including the Plus function, it operates on each list item separately > (which is exactly the opposite of what I need. For a simple example, > >> myfunc[x_, y_] = Apply[Plus, x + y]; >> myfunc[{1, 2, 3}, {4, 5, 6}] >> >> {5, 7, 9} > > When what I would really like is the number 21 (i.e., 5+7+9, perform > the > list addition first, then sum the components). In this simple example > I > could perform the summation after the function returns, but in my real > problem this would not be possible. > > When reading the documentation, it appears that the Plus function > behaves this way because it has the attribute "Flat". But even after > removing that attribute it still behaves in the same way, so I may be > misunderstanding the description of "flat". Can anyone suggest a way > to > either modify the Plus function behavior, or do this another way? > Thank > you in advance! > > Your problem has nothing to do with the attributes of Plus but is simply caused by your using = (Set) instead of := (SetDelayed). Thus: myfunc[x_,y_]:=Apply[Plus,x+y]; myfunc[{1,2,3},{4,5,6}] 21 Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/

**References**:**List arguments to functions***From:*Chris Rozell <crozell@rice.edu>