From: brabuhr@...
Date: 2010-06-08T04:12:14+09:00
Subject: Re: A better way to write this function?

On Wed, Jun 2, 2010 at 11:44 PM, Colin Bartlett <colinb2r@googlemail.com> wrote:
> On Fri, May 28, 2010 at 4:20 PM, Jason Lillywhite <
> jason.lillywhite@gmail.com> wrote:
>
>> Here is my attempt at Newton's second law in Ruby:
>>   ...
>> What if I needed more speed but still wanted it in Ruby?
>>
>
> Using C for the "fast" bits has been suggested.
>
> As an alternative to C for speed, I've found that using JRuby with parts of
> the code as Java functions works well.

I took a quick shot w/ duby-inline.

Host:
2.6.32-22-generic #33-Ubuntu SMP Wed Apr 28 13:27:30 UTC 2010 i686 GNU/Linux
Intel(R) Pentium(R) M processor 1.60GHz

Benchmark block:
100000.times{ velocity(0.5, 21.6, 600, 10, 0.0) }

"Original" code (see note below):

ruby 1.8.7 (2010-01-10 patchlevel 249) [i486-linux]
       user     system      total        real
  18.210000   0.040000  18.250000 ( 21.596111)

jruby 1.5.0 (ruby 1.8.7 patchlevel 249) (2010-05-12 6769999) (OpenJDK
Client VM 1.6.0_18) [i386-java]
       user     system      total        real
   4.525000   0.000000   4.525000 (  4.525000)

jruby 1.5.0 (ruby 1.8.7 patchlevel 249) (2010-05-12 6769999) (OpenJDK
Server VM 1.6.0_18) [i386-java]
       user     system      total        real
   3.651000   0.000000   3.651000 (  3.651000)

Duby code:

jruby 1.5.0 (ruby 1.8.7 patchlevel 249) (2010-05-12 6769999) (OpenJDK
Client VM 1.6.0_18) [i386-java]
   0.415000   0.000000   0.415000 (  0.415000)

jruby 1.5.0 (ruby 1.8.7 patchlevel 249) (2010-05-12 6769999) (OpenJDK
Server VM 1.6.0_18) [i386-java]
   0.208000   0.000000   0.208000 (  0.208000)


I had to cheat a little bit and removed the array and the block to
make it Duby-compatible:

G = 9.8

class Newton
  def rb_velocity(c, m, t, dt, vi)
    t += dt
    steps = t/dt

    i = 0
    while i < steps
      v = vi
      vi = v + ( G - c/m*v) * dt
      i += 1
    end

    vi
  end
end

And, the duby version:

require 'inline'
require 'duby_inline'

G = 9.8

class Newton
  inline :Duby do |builder|
    builder.duby "
      def db_velocity(c:double, m:double, t:int, dt:int, vi:double)
        t += dt
        steps = t/dt

        i = 0
        while i < steps
          v = vi
          vi = v + ( #{G} - c/m*v) * dt
          i += 1
        end

        vi
      end
    "
  end
end