%&(+/)&:% 10 20 40
5.71429
   (+/)&.:% 10 20 40
5.71429
   
Welcome Alex. The catch is to parenthesize (+/).

--- Den tors 4/2/10 skrev Alex Gian <[email protected]>:

> Fra: Alex Gian <[email protected]>
> Emne: [Jprogramming] A q for starters - composing without forking (% +/ %)
> Til: [email protected]
> Dato: torsdag 4. februar 2010 01.36
> Hi - complete newbie to J here.
> Though I like what I've seen so far.
> 
> Here's my starter question:
> I'd like to code the function that gives the inverse of a
> sum of
> inverses (eg. like when calculating resistors in parallel)
> 
> It works fine if I just write it out as
>     % +/ % 10 20 40     
>       (ans 5.71429)
> 
> However, if I try to make a function of it, 
>     invsuminv =. % +/ %
> it becomes a fork (I guess that _does_ make sense), and
> just computes
> the "cross-sum" of the inverses, as if I'd typed
>        (% +/ %) 10 20 40
>       0.2  0.15 0.125
>      0.15   0.1
> 0.075
>     0.125 0.075  0.05
> 
> How can I avoid this? I've tried all sorts of combinations,
> using @ and
> & but can't seem to crack it.  Obviously something
> fundamental I'm not
> grasping. Any help appreciated.
> 
> 
> 
> 
> 
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
> 

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