Re: List arguments to functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg45572] Re: List arguments to functions*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Wed, 14 Jan 2004 01:26:31 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 1/13/04 at 4:03 AM, crozell at rice.edu (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). You need to use DelayedSet rather than Set, i.e. myfunc should be defined as myfunc[x_,y_]:= Apply[Plus, x + y] With Set, you are asking Mathematica to immediately evaluate the rhs then assign that value to myfunc. Mathematica evaluates Apply[Plus, x + y] to x + y. Consequently, it is the same as if you wrote myfunc[x_,y_]=x + y. Read the discussion of DelayedSet and Set in the Mathematica book for more detail. -- To reply via email subtract one hundred and four