From: Robert Klemme <shortcutter@...>
Date: 2008-03-31T18:47:56+09:00
Subject: Re: Is it me or Math::sqrt?

2008/3/31, Phillip Gawlowski <cmdjackryan@googlemail.com>:
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>  Hello list.
>
>  I'm a bit stupefied by the different results of this algorithm I
>  implemented (Euclidean distance for 3 dimensions):
>
>  # Calculates the relative distance_to an arbitrary
>  # Note: The algorithm is not yet optimized for speed.
>  # Hopefully, it is accurate, though.
>  def distance_to(actor)
>  ~  # Stub, will use vector math or so to approximate the true distance
>  ~  distance = (self.x - actor.x)^2 + (self.y - actor.y)^2 + (self.z -
>  actor.z)^2
>  ~  Math::sqrt(distance.abs)
>  end
>
>  actor1 = Gondor::AI::Actor.new(:x => 0,:y => 0,:z => 0)
>  actor2 = Gondor::AI::Actor.new(:x => 16, :y => 16, :z => 16)
>  actor1.distance(actor2)
>  produces: 3.74165738677394
>
>  actor1 = Gondor::AI::Actor.new(:x => 1,:y => 1,:z => 1)
>  actor2 = Gondor::AI::Actor.new(:x => 15, :y => 15, :z => 15)
>  produces: 4.0
>
>  Why is that? From my understanding, these results should be identical
>  (The algebraic sign is eliminated by exponent 2, everything else is
>  addition).
>
>  Another thing that has me stumped is, that Math::sqrt requires the
>  absolute, but the result should be positive (addition of positive
>  algebraic signs).
>
>  Do I need to brush up my math more than I thought?
>
>  - -- Phillip Gawlowski
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- without words -

irb(main):002:0> (0-16)^2
=> -14
irb(main):003:0> (0-16) ** 2
=> 256

:-)

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end