Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris
 
PerlMonks  

Re^7: [OT] The statistics of hashing. (odd)

by BrowserUk (Pope)
on Apr 03, 2012 at 16:07 UTC ( #963274=note: print w/replies, xml ) Need Help??


in reply to Re^6: [OT] The statistics of hashing. (odd)
in thread [OT] The statistics of hashing.

I suspect you need to start $toggle reversed for odd values

Indeed. Using my $toggle = $P & 1 ? 1 : -1;, the output makes much more sense:

you don't show most of the code so I didn't go much further in looking

The entire code looks like this:

#! perl -slw use strict; sub PTn { my @row; for( 1 .. shift ) { push @row, 1; $row [$_] += $row [$_ - 1] for reverse 1 .. @row - 2; } return @row; } sub expN { my( $P, $N, $X ) = @_; my $xDIVn = $X / $N; my @coefs = PTn( $P+1 ); my $rv = 0; my $toggle = $P & 1 ? 1 : -1; for my $p ( reverse 1 .. $P ) { $rv += $toggle * $coefs[ $p ] * $N / $p * exp( -$p * $xDIVn ); $toggle *= -1; } return $rv + $X; } our $H //= 10; our $B //= 32; print "Using N x 2**$B vectors:"; for my $inserts ( map{ 2**$_*3/4, 2**$_ } 4 .. $B ) { printf "%10d : ", $inserts; for my $h ( 1 .. $H ) { printf "%6d ", expN( $h, 2**$B, $inserts ) - expN( $h, 2**$B, +0 ); } print ''; }

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://963274]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others about the Monastery: (2)
As of 2021-10-18 04:54 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My first memorable Perl project was:







    Results (72 votes). Check out past polls.

    Notices?