Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2004

[Date Index] [Thread Index] [Author Index]

Search the Archive

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


  • Prev by Date: Re: functions
  • Next by Date: Re: what is the general theory of extracting solutions from DSolve (and similar) functions
  • Previous by thread: Re: List arguments to functions
  • Next by thread: Re: List arguments to functions