From: mopthisandthat@... (Phidippus)
Date: 2004-04-04T01:54:36+09:00
Subject: Re: error handling

Yes, one single function is 1.5Mb. It is rediculous, but true. I tried
whether the exact same function also works in R, and it worked fine.
But R is also developed for numerical computations, so it is probably
not a fair comparison for Ruby, I suppose.

"Robert Klemme" <bob.news@gmx.net> wrote in message news:<c4hrb3$2i812u$1@ID-52924.news.uni-berlin.de>...
> "Mark Hubbart" <discord@mac.com> schrieb im Newsbeitrag
> news:789AB92E-83FE-11D8-97DE-000502FDD5CC@mac.com...
> >
> > On Apr 1, 2004, at 8:29 AM, Phidippus wrote:
> >
> > > I'm evaluating a function at various values in a for loop. The
> > > function works most of the times (99% of parameter range I am
> > > investigating), but at some values, it gives error like below and
> > > crushes. I guess something wrong with sqrt function. I'm not going to
> > > attempt to show the function here because it is 1.5Mb.
> 
> Are you serious?  A single function with 1.5MB source code?
> 
> > If I evaluate
> > > the exact same function in Maple at the value it crushed in Ruby, it
> > > behaves fine.
> 
> Well, you can't compare Ruby with Maple on this: Maple is a math system
> built to efficiency solve mathematical problems.  Ruby is more of a general
> purpose language and especially not very good at recursion.  The stack
> nesting problem surfaces every now and then.
> 
> AFAIK there is a compiler switch that you can employ during building of Ruby
> that will increase the stack size.  Alternatively you can implement sqrt as
> iterative function yourself.
> 
> > > Is there any way that when the (sqrt) function crushes, it gives some
> > > sort of error value and go on to evaluating at the next value without
> > > crushing the program? I don't want to manually restart the program at
> > > the next value each time the program crushes. In R, there is "try"
> > > function that can used for this kind of situation.
> 
> See below.
> 
> > > Thank you.
> > >
> > > #####
> > > /usr/lib/ruby/1.6/complex.rb:82:in `initialize': stack level too deep
> > > (SystemStackError)
> > >         from /usr/lib/ruby/1.6/complex.rb:63:in `new'
> > >         from /usr/lib/ruby/1.6/complex.rb:63:in `Complex'
> > >         from /usr/lib/ruby/1.6/complex.rb:130:in `/'
> > >         from /usr/lib/ruby/1.6/mathn.rb:244:in `sqrt'
> > >         from /usr/lib/ruby/1.6/mathn.rb:244:in `sqrt'
> > >         from /usr/lib/ruby/1.6/mathn.rb:244:in `sqrt'
> > >         from /usr/lib/ruby/1.6/mathn.rb:244:in `sqrt'
> > >         from /usr/lib/ruby/1.6/mathn.rb:244:in `sqrt'
> > >          ... 1461 levels...
> > >         from rubyHopf0.rb:17:in `each'
> > >         from rubyHopf0.rb:17
> > >         from rubyHopf0.rb:16:in `each'
> > >         from rubyHopf0.rb:16
> >
> > This looks like a bug... sqrt() is recursing too deeply here, 1461
> > levels seems a bit excessive. What values are causing it to dump like
> > that? Could you give a specific example?
> 
> I guess they are quite big so sqrt needs to many steps to identify the
> square root.
> 
> > Normally, you could catch an error like this:
> >
> >    begin
> >      0 / 0
> >    rescue
> >      puts "no dividing by zero in integer division!"
> >    end
> >
> > .. but that doesn't work for me with a SystemStackError. I guess those
> > are always fatal errors.
> 
> Works perfectly for me:
> 
> irb(main):036:0> def rec; rec; end
> => nil
> irb(main):037:0> begin
> irb(main):038:1*   rec
> irb(main):039:1> rescue SystemStackError => e
> irb(main):040:1>   puts "Caught it: #{e.inspect}"
> irb(main):041:1> end
> Caught it: #<SystemStackError: stack level too deep>
> => nil
> 
> Regards
> 
>     robert