From: Bil Kleb <W.L.Kleb@...>
Date: 2002-01-25T03:16:34+09:00
Subject: Modifying NArray's NVector dumps core?

Under certain conditions when we run our numerical simulation code it
dumps core as follows:

 $ ./Advect.rb -s1
 ./Vector.rb:13: [BUG] rb_gc_mark(): unknown data type 0x28(0x401ad4b0) non object
 ruby 1.6.6 (2001-12-26) [i686-linux]
 Aborted (core dumped)

Depending on the parameters we pass to the code via GetoptLong, the code
will either consistently run or consistently fail.  In addition, the
the simulation time until failure will vary; but the location of
the failure never changes: line 13 of Vector.rb.

Vector.rb defines a wrapper around NVector's constructor and
modifies the behavior of it's length and to_s methods, viz,

     1  require 'narray'
     2
     3  #  shorthand to create an NVector of floats
     4  def Vector(first, *array)
     5   NVector[first.to_f, *array]
     6  end
     7
     8  class NVector
     9   def length
    10    Math.sqrt(self**2)
    11   end
    12   def to_s
    13    to_a.join(' ')  # <<<< the failure point
    14   end
    15  end

Right now this is merely an annoyance because we can tweak the
simulation paramenters a bit one way or the other and get a completely
normal run; but, in Extreme Programming terms, this certainly doesn't
smell too good...

We are using NArray-0.5.5, and we had the same behavior when using
ruby-1.6.5.

One more bit of extraneous information: at one point we tried
turning off garbage collection and Ruby grew to over 2GB (the
size of our machine's memory) in less than 20 seconds and froze
our GNU/Linux box.  Depending on the grid size of the simulation,
Ruby (w/GC) usually only takes 15MB or so...

Thanks in advance,
--
Bil Kleb
NASA Langley Research Center
Hampton, Virginia, USA