Re: Permutation Tensor

Newsgroups	comp.lang.forth
From	Albert van der Horst <albert@spenarnc.xs4all.nl>
Subject	Re: Permutation Tensor
Date	2012-07-08 13:03 +0000
Message-ID	<m6uexj.fjr@spenarnc.xs4all.nl> (permalink)
Organization	Dutch Forth Workshop
References	<7xzk7bxrsy.fsf@ruckus.brouhaha.com> <60811296968435@frunobulax.edu> <7xpq87b0i2.fsf@ruckus.brouhaha.com>

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In article <7xpq87b0i2.fsf@ruckus.brouhaha.com>,
Paul Rubin  <no.email@nospam.invalid> wrote:
>mhx@iae.nl (Marcel Hendrix) writes:
>> all non-local implementations have approximately the same speed, and the
>> locals add a sizable overhead (because iForth doesn't inline words that
>> use locals.)
>
>Thanks, how about this?
>
>  : eps3 ( i j k -- e ) 2dup - >r -rot 2dup - >r drop - 2r> * * 2/ ;
>

I come up with this:
(now tested)

The idea is once you established that the modulo 3 sum,
you need only inspect two to find out what the eps is.

"
REQUIRE CASE-INSENSITIVE
CASE-INSENSITIVE
REQUIRE 2>R

: -ROT POSTPONE ROT POSTPONE ROT ; IMMEDIATE

: eps3 ( i j k -- e ) 2dup - >r -rot 2dup - >r drop - 2r> * * 2/ ;


\ Ensure proper mathematical mod.
: MOD'  >R S>D R> FM/MOD DROP ;

: eps2  >R 2DUP + R> + 3 MOD IF  2DROP 0  ELSE  SWAP - 1+ 3 MOD' 1- THEN ;

\ Less elegant works with floored mod too.
: eps2'  >R 2DUP + R> + 3 MOD IF  2DROP 0  ELSE  SWAP - 4 + 3 MOD 1- THEN ;

: test 4 1 DO I         4 1 DO  4 1 DO
    DUP . J . I .
    DUP  J I EPS3 .
    DUP  J I EPS2 .
    DUP  J I EPS2' .
    CR
LOOP LOOP DROP LOOP ;

"

In the FORTRAN era I hated the trick to use multiplication
to combine cases. But I'm sure your code will win hands down
on a Pentium for lack of branching.

The mod could be a table lookup, as the range is only -2..6

Groetjes Albert

--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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Permutation Tensor Arnold Doray <invalid@invalid.com> - 2012-07-05 07:13 +0000
  Re: Permutation Tensor "A. K." <akk@nospam.org> - 2012-07-05 09:25 +0200
    Re: Permutation Tensor Arnold Doray <invalid@invalid.com> - 2012-07-05 08:42 +0000
      Re: Permutation Tensor "A. K." <akk@nospam.org> - 2012-07-05 11:25 +0200
        Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-06 18:49 -0700
          Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-07 08:32 +0200
            Re: Permutation Tensor "A. K." <akk@nospam.org> - 2012-07-07 09:49 +0200
            Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 05:35 -0700
               Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-07 15:45 +0200
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 07:32 -0700
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-07 17:53 +0200
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 09:10 -0700
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-07 18:41 +0200
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 12:24 -0700
                Re: Permutation Tensor Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-07-08 07:48 +0100
                Re: Permutation Tensor Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-07-08 08:09 +0100
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-08 09:23 +0200
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-08 05:55 -0700
                Re: Permutation Tensor Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2012-07-08 20:14 +0100
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-08 13:49 -0700
                Re: Permutation Tensor Paul Rubin <no.email@nospam.invalid> - 2012-07-07 13:03 -0700
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-07 23:54 +0200
                Re: Permutation Tensor Paul Rubin <no.email@nospam.invalid> - 2012-07-07 16:43 -0700
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-08 09:07 +0200
                Re: Permutation Tensor Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-08 13:03 +0000
                Re: Permutation Tensor anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-09 14:50 +0000
                Re: Permutation Tensor m.a.m.hendrix@tue.nl - 2012-07-10 00:28 -0700
                Re: Permutation Tensor anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-10 10:11 +0000
                Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-10 21:37 +0200
                Re: Permutation Tensor anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-07-11 13:50 +0000
                Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-10 05:10 -0700
        Re: Permutation Tensor Paul Rubin <no.email@nospam.invalid> - 2012-07-06 20:46 -0700
          Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 05:36 -0700
  Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-06 18:18 -0700
    Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-06 18:33 -0700
    Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 07:28 -0700
      Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-07 08:02 -0700
  Re: Permutation Tensor Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-07 19:58 +0000
    Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-08 05:45 -0700
      Re: Permutation Tensor Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-08 20:05 +0000
  Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-08 14:24 +0200
    Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-11 07:09 +0200
      Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-11 18:42 +0200
        Re: Permutation Tensor mhx@iae.nl (Marcel Hendrix) - 2012-07-11 20:18 +0200
          Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-12 12:43 +0200
  Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-08 23:44 +0200
    Re: Permutation Tensor Krishna Myneni <krishna.myneni@ccreweb.org> - 2012-07-10 17:06 -0700
      Re: Permutation Tensor awegel@arcor.de (Alex Wegel) - 2012-07-11 07:09 +0200

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