Re^3: fibonacci numbers using subroutine?

I agree. Memoize can help a lot. Here's a little script that I use to get the 1000th, 2000th, 3000th number etc.

#!/usr/bin/perl

use strict;
use warnings;
use Math::Big qw/fibonacci/;
use Memoize;
memoize('fib', INSTALL => 'fastfib');

my $n = '1000';
print fib(), "\n";

sub fib {
    foreach  ($n) {
        my @fibonacci = fibonacci($n);
        print "$fibonacci[$n-1]", "\n";
    }
}
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Re^4: fibonacci numbers using subroutine? by Marshall (Canon) on Aug 20, 2010 at 07:49 UTC
I thought this code looked a bit odd, so I took the trouble to install Math::Big and play with it. 1. I think you have an "off by one" problem. `$fibonacci[$n-1]` does not appear to be correct. 2. The need for the fib subroutine is unclear to me. 3. This fibonacci subroutine in the Math::Big library appears to be so fast, that the need for Memoize is also unclear to me...this thing barfs out fibonacci(1000) with incredible speed! Below is my testing code: `#!/usr/bin/perl use strict; use warnings; use Math::Big qw/fibonacci/; my $n=6; print scalar(fibonacci($n)), "\n"; print "".fibonacci($n), "\n"; #another way to force scalar context my @fibs = fibonacci($n); print "@fibs\n"; print $fibs[-1],"\n"; #NOT $n-1, [$n] same as [-1] here. foreach (1000,2000,3000) { #print "".fibonacci($_), "\n\n"; #prints HUGE numbers not shown below } __END__ prints: .....testing the fibonacci of 6, which is indeed 8.... 8 8 0 1 1 2 3 5 8 8` [download] Anyway, I figure that we are getting pretty "far into the outfield" on this one. Yes, there is a library function for generating a fibonacci number. Yes, it is very fast. Yes, it can calculate these numbers to an incredible number of digits. No, it does not use a recursive algorithm. The library function likes to start the sequence at 0 instead of 1, but that is allowed within the definition of the sequence. Of course it is completely possible that I've misunderstood something - wouldn't be the first time...let me know.	[reply] [d/l] [select]

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Re^4: fibonacci numbers using subroutine?
by Marshall (Canon) on Aug 20, 2010 at 07:49 UTC

1. I think you have an "off by one" problem. $fibonacci[$n-1] does not appear to be correct.
2. The need for the fib subroutine is unclear to me.
3. This fibonacci subroutine in the Math::Big library appears to be so fast, that the need for Memoize is also unclear to me...this thing barfs out fibonacci(1000) with incredible speed!

Below is my testing code:

#!/usr/bin/perl

use strict;
use warnings;
use Math::Big qw/fibonacci/;

my $n=6;

print scalar(fibonacci($n)), "\n";
print "".fibonacci($n), "\n";  #another way to force scalar context
my @fibs = fibonacci($n);
print "@fibs\n";
print $fibs[-1],"\n";  #NOT $n-1, [$n] same as [-1] here.

foreach (1000,2000,3000)
{
   #print "".fibonacci($_), "\n\n";
   #prints HUGE numbers not shown below
}

__END__
prints:
.....testing the fibonacci of 6, which is indeed 8....
8
8
0 1 1 2 3 5 8
8
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