Seg. fault with roots(b)

[Sergei Steshenko]

--- On Mon, 5/4/09, John W. Eaton <jwe at octave.org> wrote:

> From: John W. Eaton <jwe at octave.org>
> Subject: Re: Seg. fault with roots(b)
> To: "Sergei Steshenko" <sergstesh at yahoo.com>
> Cc: "Robert Jenssen" <robertjenssen at ozemail.com.au>, "Ben Abbott" <bpabbott at mac.com>, bug-octave at octave.org
> Date: Monday, May 4, 2009, 12:23 PM
> On 27-Apr-2009, Sergei Steshenko
> wrote:
> 
> | Segfaults on my self-built 3.0.3 and 3.0.4  - 32
> bits Linux. Atlas version
> | is 3.8.2.
> | 
> | "
> | panic: Segmentation fault -- stopping myself...
> | attempting to save variables to `octave-core'...
> | save to `octave-core' complete
> | ".
> 
> So is this a bug in ATLAS 3.8.x or a change in the
> interface to some
> LAPACK subroutine, or what?
> 
> It might help if someone who can reproduce the problem
> would run
> Octave under GDB and find precisely where the crash occurs,
> and maybe
> diagnose why the crash is happening.  Are we calling
> an LAPACK
> function incorrectly?  Not passing sufficient
> workspace?  What?
> 
> jwe
>  

I am illiterate WRT gdb - have been able to find and fix my bugs using
diagnostic print statements, bu here is an additional piece of info:

"
octave:1> roots(rand(1, 11))
ans =

   0.86681 + 0.42220i
   0.86681 - 0.42220i
   0.45553 + 0.83569i
   0.45553 - 0.83569i
  -0.13974 + 1.04788i
  -0.13974 - 1.04788i
  -1.04699 + 0.28372i
  -1.04699 - 0.28372i
  -0.63653 + 0.55502i
  -0.63653 - 0.55502i

octave:2> roots(rand(1, 12))
ans =

   0.66823 + 0.81868i
   0.66823 - 0.81868i
   0.80950 + 0.46852i
   0.80950 - 0.46852i
  -0.00880 + 1.08928i
  -0.00880 - 1.08928i
  -0.63962 + 0.93444i
  -0.63962 - 0.93444i
  -0.74431 + 0.40461i
  -0.74431 - 0.40461i
  -0.83676 + 0.00000i

octave:3> roots(rand(1, 13))
panic: Segmentation fault -- stopping myself...
attempting to save variables to `octave-core'...
save to `octave-core' complete
".

I.e. it appears the crash occurs from polynomial degree 12 and above.

I do not know what the interface to ATLAS is, but it doesn't look likely
there is a change at 12.

By the way, 'help' example works:

"
octave:4> help roots
 -- Function File:  roots (V)
     For a vector V with N components, return the roots of the
     polynomial

          v(1) * z^(N-1) + ... + v(N-1) * z + v(N)

     As an example, the following code finds the roots of the quadratic
     polynomial
          p(x) = x^2 - 5.

          c = [1, 0, -5];
          roots(c)
          =>  2.2361
          => -2.2361
     Note that the true result is +/- sqrt(5) which is roughly +/-
     2.2361.

     See also: compan.

Overloaded function:

   groots (galois, ...)

roots is a built-in function

Additional help for built-in functions and operators is
available in the on-line version of the manual.  Use the command
`doc <topic>' to search the manual index.

Help and information about Octave is also available on the WWW
at http://www.octave.org and via the help at octave.org
mailing list.
octave:5>           c = [1, 0, -5];
octave:6>           roots(c)
ans =

  -2.2361
   2.2361

octave:7>           
".

Regards,
  Sergei.