From bug-octave-request at bevo dot che dot wisc dot edu  Fri Jan 29 02:28:09 1999
Subject: Bessel Functions of the Second Kind Crash
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: "Rafael R. Sevilla 94-22131" <rsevilla at eee dot upd dot edu dot ph>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Fri, 29 Jan 1999 02:20:45 -0600 (CST)

On 29-Jan-1999, Rafael R. Sevilla 94-22131 <rsevilla at eee dot upd dot edu dot ph> wrote:

| Bug report for Octave 2.0.13 configured for i386-redhat-linux-gnu
| 
| Description:
| -----------
| 
|   * Using the Bessel functions of the second kind (bessely) crashes Octave,
|     given arguments which are nonzero for order zero.
|   * Bessel Y for zero arguments for any order (including zero) give a
|     misleading error message (I think it should return -inf and warn of a
|     singularity, see below)
| 
| Repeat-By:
| ---------
| 
| octave:1> bessely(0,x)
| 
| for any nonzero value of x will instantly crash Octave with a segmentation
| fault.  The octave-core file is empty.
| 
| Bessel Y with zero arguments for any order gives a cryptic and misleading error
| message:
| 
| octave:1> bessely(n,0)
| error: bessely: error computing function values
| error: evaluating index expression near line 1, column 1
| 
| where n is any order number (this happens even for order zero).  This doesn't
| return anything!  The Bessel functions of the second kind have a singularity
| at zero and in this case it should act like the csc(x) function and return
| -Inf as its function value and warn about a singularity.

These problems should be fixed in the current test release which uses
new code for Bessel functions that can handle a lot more cases than
the old stuff:

  $ src/octave 
  Octave, version 2.0.13.96 (i686-pc-linux-gnulibc1).
  Copyright (C) 1996, 1997, 1998 John W. Eaton.
  This is free software with ABSOLUTELY NO WARRANTY.
  For details, type `warranty'.

  octave:1> bessely (0, 1)
  ans = 0.088257
  octave:2> bessely (0,0)
  ans = -Inf
  octave:3> bessely (1,0)
  ans = -Inf

The test releases are available at ftp.che.wisc.edu in the directory
/pub/octave/test-releases.

| Besides, where's the
| 'index expression' there?

Anything that looks like x(args) is an `index expression' to Octave.
It's too bad that Matlab didn't distinguish variable indexing and
function calls using different operators (e.g., [] for indexing and ()
for function calls).  Oh well...

| (Sorry.  I've never been able to compile the sources for Octave on
| my machine.  If GCC doesn't sig 11 it comes up with a mysterious
| error message somewhere that I don't see when compiling anything
| else.

Sorry, random sig11 when using gcc sounds like bad hardware.

| This has happened for Octave 1.1.1 on my old Slackware
| machine and for Octave 2.0.11 and 2.0.13 on my current Red Hat
| machine.  And while I'd like to think I have a lot of knowledge on
| numerical algorithms, I have a real distaste for C++ programming
| bordering on "religious intolerance.")

My apologies for not consulting you when I chose the implementation
language.

jwe