Beefy Boxes and Bandwidth Generously Provided by pair Networks
Don't ask to ask, just ask

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

Using the dependency graph I posted earlier, I was able to construct a non-recursive implementation of the Ackermann function. It visits the graph left to right, top to bottom.

use strict; use warnings; use feature qw( say ); sub A { my ($m, $n) = @_; # $A[$m] holds A($m, $n[$m]) my (@n, @A); for my $mi (0..$m) { $n[$mi] = -1; $A[$mi] = 1; } for (;;) { ++$n[0]; $A[0] = $n[0] + 1; for my $mi (1..$m) { last if $A[$mi] != $n[$mi-1]; $A[$mi] = $A[$mi-1]; ++$n[$mi]; } return $A[$m] if $n[$m] == $n; } } say A(@ARGV);

Maybe you'll have better luck with that.

Some properties:

  • It only keeps m+1 Ackermann numbers in memory at once.
  • It never calculates the same Ackermann number twice.

m<4 can be special-cased. Known formula exist for A(0,n), A(1,n), A(2,n) and A(3,n).

Update: Cleaned up code a bit.

In reply to Re: Non-recursive Ackermann by ikegami
in thread [OT]: threading recursive subroutines. by BrowserUk

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others about the Monastery: (4)
    As of 2018-06-24 05:42 GMT
    Find Nodes?
      Voting Booth?
      Should cpanminus be part of the standard Perl release?

      Results (126 votes). Check out past polls.