> From: Roger Hui <[email protected]>
>
> It is not in the Special Code section because there is
> nothing special about its implementation.
> There are examples of code that are even neater but are
> not "special" and so are not in Appendix B. For example, A. .
> http://www.jsoftware.com/jwiki/Essays/Permutation_Index
>
> From: Zsbán Ambrus
>
> > On Fri, Feb 19, 2010 at 4:37 PM, Roger Hui wrote:
> > > The timings wouldn't be as follows if u/\. were quadratic:
> > > ----- Original Message -----
> > >> Is there any chance that a future J version would optimize
> > the monad
> > >> u/\. for any verb u to make only linear number of calls to u
> > instead>> of quadratic?
> >
> > Wow, it's like that indeed, in the version I've got too. Sorry.
> >
> > However, I don't see this documented in the Special Code listing of
> > the Dictionary. Could you point me to where this is
> > documented, or
> > document this?
Here's a simple mechanism to show how things work:
argument tracing.
plus=: 4 : 'x + y [ smoutput x,y' NB. define a tracer
plus /\. 1 10 100 1000 10000 NB. use illustrative data
1000 10000 NB. linear algorithm
100 11000
10 11100
1 11110
11111 11110 11100 11000 10000
plus /\ 1 10 100 NB. "triangular" algorithm
1 10
10 100
1 110
1 11 111
plus /\ 1 10 100 1000
1 10 (a)
10 100 --+
1 110 <-+ (b)
100 1000 --+
10 1100 <-+ --+
1 1110 <-+ (c)
1 11 111 1111
(a)(b) (c)
plus /\ 1 10 100 1000 10000
1 10 (a)
10 100 --+
1 110 <-+ (b)
100 1000 --+
10 1100 <-+ --+
1 1110 <-+ (c)
1000 10000 --+
100 11000 <-+ --+
10 11100 <-+ --+
1 11110 <-+ (d)
1 11 111 1111 11111
(a)(b) (c) (d)
A variation with arguments and result:
plus=: 4 : '(] ([smoutput) x,y,]) x + y'
plus /\ 1 10 100 1000
1 10 11
10 100 110
1 110 111
100 1000 1100
10 1100 1110
1 1110 1111
1 11 111 1111
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
