Re: [FWP] Factorial Elegance

[Michael G Schwern <schwern@pobox.com>]

On Fri, Sep 15, 2000 at 09:00:33AM -0500, Tim Ayers wrote:
> I benchmarked calculating 170!. I did it with and without caching,
> i.e. in Michael's and my solution I reset the cache before calling
> factorial(170). I'm really impressed at the speed of Michael's
> solution. How in the world is it so fast?

I noticed that your two benchmarks were nearly the same, regardless of
caching, which ain't right.  For some reason, using a string to
benchmark (ie. schwern => '%factorial = (); schwern(170)') wasn't
clearing the caches.  If you did it in a subroutine, (schwern => sub {
%factorial = (); schwern(170) }) then things work.

I never anticipated anyone clearing Tie::Math's cache, so the thing
seems to fall apart if you do so "Out of memory during "large" request
for 134221824 bytes".  I'll have to figure out why that is.


> So as always, my solution is mediocre, but my initial reaction to
> Michael's answer was, "If I wanted to write code like that, I'd learn
> Prolog." ;-)

It was actually inspired in a discusion with my old boss about
memoization.  He mentioned that in Mathematica you can just write out
a function, and it would figure it out including caching.  At the time
I was looking for an excuse to use lvalue subroutines, so tada!

-- 

Michael G Schwern      http://www.pobox.com/~schwern/      schwern@pobox.com
Just Another Stupid Consultant                      Perl6 Kwalitee Ashuranse
<GuRuThuG> make a channel called Perl, and infest it with joking and
fun....it doesnt make alot of sense.

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