Your skill will accomplishwhat the force of many cannot PerlMonks

### comment on

 Need Help??
Two points. I found that if I used Math::BigFloat in the choose function, I got round off errors; errors I didn't get when using Math::BigInt.

Second, I got a much better performance for the choose function if I didn't calculate 3 factorials, but just one, and did some multiplication myself. The further the second argument is away from half of the first argument, the bigger the advantage. Here's a benchmark:

```#!/usr/bin/perl

use strict;
use warnings;

use Math::BigFloat;
use Benchmark qw /timethese cmpthese/;

#
# choose (n, k) == n! / ((n - k)! * k!) == n! / (n - k)! / k!
#               == n * (n - 1) * ... * (n - k + 1) / k!

sub choose_fac {
my (\$n, \$k) = @_;

Math::BigInt -> new (\$n) -> bfac            /
Math::BigInt -> new (\$n - \$k) -> bfac /
Math::BigInt -> new (\$k)      -> bfac
}

sub choose_mul {
my (\$n, \$k) = @_;

\$k = \$n - \$k if \$k > \$n - \$k;  # Make the loop smaller;
# we can do this because
# choose (n, k) == choose (n, n - k
+).

my \$p       = Math::BigInt -> new (1);
my \$start   = \$n - \$k + 1;

for (my \$i = \$start; \$i <= \$n; \$i ++) {
\$p *= \$i;
}

\$p / Math::BigInt -> new (\$k) -> bfac;
}

our (@r1, @r2);
our  @pairs = map {[/(\d+)\s+(\d+)/]} <DATA>;

cmpthese -10 => {
fac      => '@r1 = map {choose_fac @\$_} @pairs',
mul      => '@r2 = map {choose_mul @\$_} @pairs',
};

die "Unequal" unless "@r1" eq "@r2";

__DATA__
1000    0
1000  100
1000  500
1000 1000

s/iter  fac  mul
fac   2.08   -- -89%
mul  0.226 824%   --

Abigail

Title:
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.
• 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: & & < < > > [ [ ] ]
• Link using PerlMonks shortcuts! What shortcuts can I use for linking?

Create A New User
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others browsing the Monastery: (5)
As of 2020-12-02 00:16 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
How often do you use taint mode?

Results (25 votes). Check out past polls.

Notices?