From bug-octave-request at che dot utexas dot edu  Sun Oct 24 13:11:34 1993
Subject: 0.75.1: SIGSEGV when using clear to force reload
From: iwj10 at cus dot cam dot ac dot uk (Ian Jackson)
To: bug-octave at che dot utexas dot edu
Date: Sun, 24 Oct 93 11:57 GMT

I'm running a binary distribution of Octave 0.75.1 under Linux
0.99pl13 on a no-name 486DX/33.  Octave gets a segmentation fault when
I try to use `clear' to force reloading of a function defined in an
M-file.

Reproduce as follows:

Create the following file and call it `makei.m':

function I = makei ( L )
  n = rows(L)
  C = sum(L)'
  U = diag(C) - (C * ones(1,n))'
  invU = inv(U)
  cumI = zeros(n) ;
  B = -ones(n,1) / n ;
  p=1
  while (p < n)
    B(p)= 1 - 1/n ;
    V = invU * B
    Vmat = V*ones(1,n) ;
    F = (XX - XX) .* L
    cumI = cumI + F ;
    B(p)= 1/n ;
    p=p+1
  endwhile
  I = CI
endfunction

Now run octave:
$ octave 
Octave, version 0.75.1.  Copyright (C) 1992, 1993, John W. Eaton.
This is free software with ABSOLUTELY NO WARRANTY.
For details, type `warranty'.

octave:1> L=[0 1; 1 0]
L =

  0  1
  1  0

octave:2> makei(L)
error: `XX' undefined

n = 2
(rest of output deleted for brevity)

octave:2> clear makei

At this point, without exiting Octave, edit the file makei.m, changing
the two occurrences of XX to Vmat, producing the following contents:

function I = makei ( L )
  n = rows(L)
  C = sum(L)'
  U = diag(C) - (C * ones(1,n))'
  invU = inv(U)
  cumI = zeros(n) ;
  B = -ones(n,1) / n ;
  p=1
  while (p < n)
    B(p)= 1 - 1/n ;
    V = invU * B
    Vmat = V*ones(1,n) ;
    F = (Vmat - Vmat') .* L
    cumI = cumI + F ;
    B(p)= 1/n ;
    p=p+1
  endwhile
  I = CI
endfunction

Now go back to Octave and try to run the changed function:

octave:3> makei(L)
error: caught SIGSEGV -- stopping myself...

Viola!

Unfortunately I do not have available to me the command line arguments
to configure, and it doesn't leave a corefile (despite the working
directory being writeable) so I can't send you a stack backtrace.

This particular distribution of Octave has crashed in this way several
times under different circumstances; this is the first error I have
been able to repeat.

The tarfile containing the distribution had all the files owned by
user `btenison', group `users', and it looks like it was compiled on
September the 26th, if that's any help.