From: "Shot (Piotr Szotkowski)" <shot@...>
Date: 2009-11-22T06:30:47+09:00
Subject: Re: Finding the closest value from a matrix

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Mahadev Ittina:

> They are limited to those spacings and those diameters, as they
> are industry standards. However there are 5 more higher spacings.

That=E2=80=99s ok, then the matrix is small enough to be kept in memory
(and you can pregenerate it and only search on runtime, of course):

# pregenerate
diameters =3D [8, 10, 12, 16]
spacings  =3D [85, 90, 100, 125, 150, 175] # extend as needed
values    =3D diameters.product(spacings).map { |d, s| [0.5 * Math::PI * d =
** 2 / s, d, s] }.sort

# search
values.find { |x,| x > 1.1 } # =3D> [1.11701072127637, 8, 90]
values.find { |x,| x > 2 }   # =3D> [2.26194671058465, 12, 100]

> So basically you are creating a map? That's filled with the values?

I=E2=80=99m mapping every diameter+spacing pair to [value, diameter, spacin=
g]
triple, then I=E2=80=99m sorting the triples and picking the first one with=
 the
first element (the value) larger than the desired input.

> Thats quiet interesting. I tried the exact same thing, it says
> "undefined method 'product' for for [8, 10, 12, 16]:Array"

The above works in Ruby 1.8.7 and 1.9.1.

If you run an earlier Ruby 1.8 version, you can either use the
backports gem=C2=B9 or implement a simple variation tailored to your case:

class Array
  def product other
    inject([]) do |result, my|
      result.concat other.map { |their| [my, their] }
    end
  end unless method_defined? :product
end

[:a, :b].product [:c, :d]
# =3D> [[:a, :c], [:a, :d], [:b, :c], [:b, :d]]

=C2=B9 http://github.com/marcandre/backports

=E2=80=94 Shot
--=20
Deleted code is debugged code.
                 [Jeff Sickel]

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