[Bug-gsl] [bug #42220] Division by zero in "hybrid*" when initial guess is root

[Patrick Alken]

URL:
  <http://savannah.gnu.org/bugs/?42220>

                 Summary: Division by zero in "hybrid*" when initial guess is
root
                 Project: GNU Scientific Library
            Submitted by: psa
            Submitted on: Mon 28 Apr 2014 03:43:33 PM GMT
                Category: Runtime error
                Severity: 3 - Normal
        Operating System: 
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 
         Discussion Lock: Any

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Details:

Hello GSL team,

The GSL implementations of the "Hybrid" family of multidimensional
rootfinders from MINPACK contain a bug where they divide by zero when the
initial guess happens to be the root.  This affects the "fsolver" types
"hybrid" and "hybrids" as well as the "fdfsolver" types "hybridj" and
"hybridsj".  This results in a floating point exception if trapping is
enabled.

I have attached a small program (bug_hybrid.c), based on the manual's
example code, that triggers this bug when GSL_IEEE_MODE=trap-common.  The
current output is:

    GSL_IEEE_MODE="trap-common"
    type = hybrid
    Floating point exception (core dumped)

The expected output is:

    GSL_IEEE_MODE="trap-common"
    type = hybrid
      status = success
      root = 1.000000e+00
    type = hybrids
      status = success
      root = 1.000000e+00
    type = hybridj
      status = success
      root = 1.000000e+00
    type = hybridsj
      status = success
      root = 1.000000e+00


I'll note that when I originally discovered this bug, a colleague of mine
claimed that the problem is not present in the original FORTRAN
implementation in MINPACK, but rather was introduced in the GSL port.

Thank you for looking into this, and if you have any questions, just let me
know.

 - Curran



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File Attachments:


-------------------------------------------------------
Date: Mon 28 Apr 2014 03:43:33 PM GMT  Name: bug_hybrid.c  Size: 3kB   By: psa

<http://savannah.gnu.org/bugs/download.php?file_id=31266>

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