@c Copyright (C) 1992 John W. Eaton
@c This is part of the Octave manual.
@c For copying conditions, see the file gpl.texi.

@c The text of this file will eventually appear in the file BUGS
@c in the Octave distribution, as well as in the Octave manual.

@ifclear BUGSONLY
@node Trouble, Concept Index, Installation, Top
@chapter Known Causes of Trouble with Octave
@end ifclear
@cindex bugs, known
@cindex installation trouble
@cindex known causes of trouble
@cindex troubleshooting

This section describes known problems that affect users of Octave.  Most
of these are not Octave bugs per se---if they were, we would fix them.
But the result for a user may be like the result of a bug.

Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.

@menu
* Actual Bugs::                 Bugs we will fix later.
* Installation Problems::       Problems that manifest when you install Octave.
* Disappointments::             Regrettable things we can't change.
* Reporting Bugs::              
* Bug Criteria::                
* Bug Lists::                   
* Bug Reporting::               
* Sending Patches::             
* Service::                     
@end menu

@node Actual Bugs, Installation Problems,  , Trouble
@section Actual Bugs We Haven't Fixed Yet

@itemize @bullet
@item
Recursive function calls are not currently allowed.
@end itemize

@node Installation Problems, Disappointments, Actual Bugs, Trouble
@section Installation Problems
	
This is a list of problems (and some apparent problems which don't
really mean anything is wrong) that may show up during installation of
Octave.

@c XXX FIXME XXX --- this might be a good place to explain the terms for
@c FSQP and NPSOL.

@itemize @bullet
@item
Problems with finite and isinf on systems that don't have @code{isinf()}
but do have @code{finite()}.

The copy of @file{math.h} supplied with libg++ version 2.3 (and possibly
other versions as well) declares @code{finite()} as
@example
double finite (double);
@end example
even though some (many? all?) systems declare it as
@example
int finite (double);
@end example

If the copy of @file{math.h} from libg++ was installed, you should edit
it so that the libg++ declaration of @samp{finite()} matches the
system's.

@item
Problems compiling octave.cc on RS/6000 (and possibly other)
systems:

If octave.cc fails to compile due to parse errors in system include
files and undeclared subroutines like `gethostname' and `endpwent',
it is probably because not all of the libg++ include files have been
installed.  This appears to be a problem with libg++ version 2.3.
Here's a fix:

Apply the following patch to @file{libg++/config/rs6000.mh} and re-run
make install for libg++.

@example
*** rs6000.mh~  Mon Aug 17 19:18:44 1992
--- rs6000.mh   Mon Dec 28 23:54:57 1992
***************
*** 3,6 ****
  # /usr/include/unistd.h has write(int, char*, unsigned) instead
  # of write(int, const void*, size_t).  This causes problems due
  # to g++ new pedantic dis-allowal of void* -> char* conversions.
! G_CONFIG_ARGS = "HAVE_UNISTD=0 /*broken*/"
\ No newline at end of file
--- 3,11 ----
  # /usr/include/unistd.h has write(int, char*, unsigned) instead
  # of write(int, const void*, size_t).  This causes problems due
  # to g++ new pedantic dis-allowal of void* -> char* conversions.
! G_CONFIG_ARGS = "HAVE_UNISTD=0 /*broken*/"
! 
! # If the C include files are C++-ready (with extern "C"),
! # define: HAVE_CPLUS_EXTERN = 1 and: WRAP_C_INCLUDES =
! # If not, define HAVE_CPLUS_EXTERN = 0, and do not define WRAP_C_INCLUDES here
.
! HAVE_CPLUS_EXTERN = 0
@end example

@item
Lots of warnings about `control reaches end of non-void function'
when compiling with -O.

This appears to be a problem with g++ and the definition of an empty
destructor in Complex.h from libg++.  Deleting the declaration and
definition of the (unnecessary) destructor from Complex.h eliminates
the warnings.

@item
If you don't have NPSOL but you still want to be able to solve NLPs, or
if you don't have QPSOL but you still want to solve QPs, you'll need to
find replacements or order them from Stanford.  If you know of a freely
redistributable replacement, please let us know---we might be interested
in distributing it with Octave.

You can get more information about NPSOL and QPSOL from

@quotation
Stanford University@*
Office of Technology Licensing@*
857 Serra Street@*
Stanford CA 94305-6225@*
Tel: (415) 723-0651@*
Fax: (415) 725-7295
@end quotation

Octave may soon support FSQP, an NLP solver from Andre Tits
(andre@@src.umd.edu) of the University of Maryland.  FSQP is available
free of charge to academic sites, but can not be redistributed to third
parties.
@end itemize

@node Disappointments, Reporting Bugs, Installation Problems, Trouble
@section Disappointments and Misunderstandings

These problems are perhaps regrettable, but we don't know any practical
way around them.

@node Reporting Bugs, Bug Criteria, Disappointments, Trouble
@section Reporting Bugs
@cindex bugs
@cindex reporting bugs

Your bug reports play an essential role in making Octave reliable.

When you encounter a problem, the first thing to do is to see if it is
already known.  @xref{Trouble}.  If it isn't known, then you should
report the problem.

Reporting a bug may help you by bringing a solution to your problem, or
it may not.  In any case, the principal function of a bug report is
to help the entire community by making the next version of Octave work
better.  Bug reports are your contribution to the maintenance of Octave.

In order for a bug report to serve its purpose, you must include the
information that makes it possible to fix the bug.

@menu
* Bug Criteria::                
* Where: Bug Lists.             Where to send your bug report.
* Reporting: Bug Reporting.     How to report a bug effectively.
* Patches: Sending Patches.     How to send a patch for Octave.
@end menu

@node Bug Criteria, Bug Lists, Reporting Bugs, Trouble
@section Have You Found a Bug?
@cindex bug criteria

If you are not sure whether you have found a bug, here are some guidelines:

@itemize @bullet
@cindex fatal signal
@cindex core dump
@item
If Octave gets a fatal signal, for any input whatever, that is
a bug.  Reliable interpreters never crash.

@cindex incorrect output
@cindex incorrect results
@cindex results, incorrect
@cindex answers, incorrect
@cindex erroneous results
@cindex wrong answers
@item
If Octave produces incorrect results, for any input whatever,
that is a bug.

@cindex undefined behavior
@cindex undefined function value
@item
Some output may appear to be incorrect when it is in fact due to a
program whose behavior is undefined, which happened by chance to give
the desired results on another system.  For example, the range operator
may produce different results because of differences in the way floating
point arithmetic is handled on various systems.

@cindex erroneous messages
@cindex incorrect error messages
@cindex error messages, incorrect
@item
If Octave produces an error message for valid input, that is a bug.

@cindex invalid input
@item
If Octave does not produce an error message for invalid input, that is
a bug.  However, you should note that your idea of ``invalid input''
might be my idea of ``an extension'' or ``support for traditional
practice''.

@cindex improving Octave
@ suggestions
@item
If you are an experienced user of programs like Octave, your suggestions
for improvement are welcome in any case.
@end itemize

@node Bug Lists, Bug Reporting, Bug Criteria, Trouble
@section Where to Report Bugs
@cindex bug report mailing lists
@cindex reporting bugs
@cindex bugs, reporting

Send bug reports for Octave to:

@example
bug-octave@@che.utexas.edu
@end example

@strong{Do not send bug reports to @samp{help-octave}}.  Most users of
Octave do not want to receive bug reports.  Those that do, have asked to
be on @samp{bug-octave}.

As a last resort, send bug reports on paper to:

@example
Octave Bugs c/o John W. Eaton
Department of Chemical Engineering
The University of Texas at Austin
Austin, Texas 78712
@end example

@node Bug Reporting, Sending Patches, Bug Lists, Trouble
@section How to Report Bugs
@cindex bugs, reporting

The fundamental principle of reporting bugs usefully is this:
@strong{report all the facts}.  If you are not sure whether to state a
fact or leave it out, state it!

Often people omit facts because they think they know what causes the
problem and they conclude that some details don't matter.  Thus, you might
assume that the name of the variable you use in an example does not matter.
Well, probably it doesn't, but one cannot be sure.  Perhaps the bug is a
stray memory reference which happens to fetch from the location where that
name is stored in memory; perhaps, if the name were different, the contents
of that location would fool the interpreter into doing the right thing
despite the bug.  Play it safe and give a specific, complete example.
That is the easiest thing for you to do, and the most helpful.

Keep in mind that the purpose of a bug report is to enable someone to
fix the bug if it is not known.  It isn't very important what happens if
the bug is already known.  Therefore, always write your bug reports on
the assumption that the bug is not known.

Sometimes people give a few sketchy facts and ask, ``Does this ring a
bell?''  This cannot help us fix a bug, so it is basically useless.  We
respond by asking for enough details to enable us to investigate.
You might as well expedite matters by sending them to begin with.

Try to make your bug report self-contained.  If we have to ask you for
more information, it is best if you include all the previous information
in your response, as well as the information that was missing.

To enable someone to investigate the bug, you should include all these
things:

@itemize @bullet
@item
The version of Octave.  You can get this by noting the version number
that is printed when Octave starts, or running it with the @samp{-v}
option.

Without this, we won't know whether there is any point in looking for
the bug in the current version of Octave.

@item
A complete input file that will reproduce the bug.

A single statement may not be enough of an example---the bug might
depend on other details that are missing from the single statement where
the error finally occurs.

Without a real example one can execute, all anyone can do about your bug
report is wish you luck.  It would be futile to try to guess how to
provoke the bug.

@item
The command arguments you gave Octave to execute that example
and observe the bug.  To guarantee you won't omit something important,
list all the options. 

If we were to try to guess the arguments, we would probably guess wrong
and then we would not encounter the bug.

@item
The type of machine you are using, and the operating system name and
version number.

@item
The command-line arguments you gave to the @code{configure} command when
you installed the interpreter.

@item
A complete list of any modifications you have made to the interpreter
source.  (We don't promise to investigate the bug unless it happens in
an unmodified version of Octave.  But if you've made modifications and
don't tell us, then you are sending us on a wild goose chase.)

Be precise about these changes---show a context diff for them.

Adding files of your own (such as a machine description for a machine we
don't support) is a modification of the interpreter source.

@item
Details of any other deviations from the standard procedure for installing
Octave.

@cindex incorrect output
@cindex incorrect results
@cindex results, incorrect
@cindex answers, incorrect
@cindex erroneous results
@cindex wrong answers
@item
A description of what behavior you observe that you believe is
incorrect.  For example, "The interpreter gets a fatal signal," or, "The
output produced at line 208 is incorrect."

Of course, if the bug is that the interpreter gets a fatal signal, then
one can't miss it.  But if the bug is incorrect output, the maintainer
might not notice unless it is glaringly wrong.  None of us has time to
study all the code from a 50-line program just on the chance that one
instruction might be wrong.  We need `you' to do this part!

Even if the problem you experience is a fatal signal, you should still
say so explicitly.  Suppose something strange is going on, such as, your
copy of the interpreter is out of synch, or you have encountered a bug
in the C library on your system.  Your copy might crash and the copy
here would not.  If you said to expect a crash, then when the
interpreter here fails to crash, we would know that the bug was not
happening.  If you don't say to expect a crash, then we would not know
whether the bug was happening.  We would not be able to draw any
conclusion from our observations.

Often the observed symptom is incorrect output when your program is run.
Sad to say, this is not enough information unless the program is short
and simple.  None of us has time to study a large program to figure out
how it would work if compiled correctly, much less which line of it was
interpreted incorrectly.  So you will have to do that.  Tell us which
source line it is, and what incorrect result happens when that line is
executed.  A person who understands the program can find this as easily
as finding a bug in the program itself.

@item
If you wish to suggest changes to the Octave source, send them as
context diffs.  If you even discuss something in the Octave source,
refer to it by context, not by line number.

The line numbers in the development sources don't match those in your
sources.  Your line numbers would convey no useful information to the
maintainers.

@item
Additional information from a debugger might enable someone to find a
problem on a machine which he does not have available.  However, you
need to think when you collect this information if you want it to have
any chance of being useful.
@end itemize

Here are some things that are not necessary:

@itemize @bullet
@cindex bugs, investigating
@item
A description of the envelope of the bug.

Often people who encounter a bug spend a lot of time investigating which
changes to the input file will make the bug go away and which changes
will not affect it.

This is often time consuming and not very useful, because the way we
will find the bug is by running a single example under the debugger with
breakpoints, not by pure deduction from a series of examples.  You might
as well save your time for something else.

Of course, if you can find a simpler example to report @emph{instead} of
the original one, that is a convenience.  Errors in the output will be
easier to spot, running under the debugger will take less time, etc.
Most Octave bugs involve just one function, so the most straightforward
way to simplify an example is to delete all the function definitions
except the one where the bug occurs.  Those earlier in the file may be
replaced by external declarations if the crucial function depends on
them.

However, simplification is not vital; if you don't want to do
this, report the bug anyway and send the entire test case you
used.

@item
A patch for the bug.

A patch for the bug is useful if it is a good one.  But don't omit the
necessary information, such as the test case, on the assumption that a
patch is all we need.  We might see problems with your patch and decide
to fix the problem another way, or we might not understand it at all.

Sometimes with a program as complicated as Octave it is very hard to
construct an example that will make the program follow a certain path
through the code.  If you don't send the example, we won't be able to
construct one, so we won't be able to verify that the bug is fixed.

And if we can't understand what bug you are trying to fix, or why your
patch should be an improvement, we won't install it.  A test case will
help us to understand.

@cindex bugs, guessing causes
@item
A guess about what the bug is or what it depends on.

Such guesses are usually wrong.  Even I can't guess right about such
things without first using the debugger to find the facts.
@end itemize

@node Sending Patches, Service, Bug Reporting, Trouble
@section Sending Patches for Octave
@cindex improving Octave
@cindex diffs, submitting
@cindex patches, submitting
@cindex submitting diffs
@cindex submitting patches

If you would like to write bug fixes or improvements for Octave, that is
very helpful.  When you send your changes, please follow these
guidelines to avoid causing extra work for us in studying the patches.

If you don't follow these guidelines, your information might still be
useful, but using it will take extra work.  Maintaining Octave is a lot
of work in the best of circumstances, and we can't keep up unless you do
your best to help.

@itemize @bullet
@item
Send an explanation with your changes of what problem they fix or what
improvement they bring about.  For a bug fix, just include a copy of the
bug report, and explain why the change fixes the bug.

(Referring to a bug report is not as good as including it, because then
we will have to look it up, and we have probably already deleted it if
we've already fixed the bug.)

@item
Always include a proper bug report for the problem you think you have
fixed.  We need to convince ourselves that the change is right before
installing it.  Even if it is right, we might have trouble judging it if
we don't have a way to reproduce the problem.

@item
Include all the comments that are appropriate to help people reading the
source in the future understand why this change was needed.

@item
Don't mix together changes made for different reasons.
Send them @emph{individually}.

If you make two changes for separate reasons, then we might not want to
install them both.  We might want to install just one.  If you send them
all jumbled together in a single set of diffs, we have to do extra work
to disentangle them---to figure out which parts of the change serve
which purpose.  If we don't have time for this, we might have to ignore
your changes entirely.

If you send each change as soon as you have written it, with its own
explanation, then the two changes never get tangled up, and we can
consider each one properly without any extra work to disentangle them.

Ideally, each change you send should be impossible to subdivide into
parts that we might want to consider separately, because each of its
parts gets its motivation from the other parts.

@item
Send each change as soon as that change is finished.  Sometimes people
think they are helping us by accumulating many changes to send them all
together.  As explained above, this is absolutely the worst thing you
could do.

Since you should send each change separately, you might as well send it
right away.  That gives us the option of installing it immediately if it
is important.

@item
Use @samp{diff -c} to make your diffs.  Diffs without context are hard
for us to install reliably.  More than that, they make it hard for us to
study the diffs to decide whether we want to install them.  Unidiff
format is better than contextless diffs, but not as easy to read as
@samp{-c} format.

If you have GNU diff, use @samp{diff -cp}, which shows the name of the
function that each change occurs in.

@item
Write the change log entries for your changes.  We get lots of changes,
and we don't have time to do all the change log writing ourselves.

Read the @file{ChangeLog} file to see what sorts of information to put
in, and to learn the style that we use.  The purpose of the change log
is to show people where to find what was changed.  So you need to be
specific about what functions you changed; in large functions, it's
often helpful to indicate where within the function the change was.

On the other hand, once you have shown people where to find the change,
you need not explain its purpose. Thus, if you add a new function, all
you need to say about it is that it is new.  If you feel that the
purpose needs explaining, it probably does---but the explanation will be
much more useful if you put it in comments in the code.

If you would like your name to appear in the header line for who made
the change, send us the header line.

@item
When you write the fix, keep in mind that I can't install a change that
would break other systems.

People often suggest fixing a problem by changing machine-independent
files to do something special that a particular system needs.  Sometimes
it is totally obvious that such changes would break Octave for almost
all users.  We can't possibly make a change like that.  At best it might
tell us how to write another patch that would solve the problem
acceptably.

Sometimes people send fixes that @emph{might} be an improvement in
general---but it is hard to be sure of this.  It's hard to install
such changes because we have to study them very carefully.  Of course,
a good explanation of the reasoning by which you concluded the change
was correct can help convince us.

Please help us keep up with the workload by designing the patch in a
form that is good to install.
@end itemize

@node Service,  , Sending Patches, Trouble
@section How To Get Help with Octave
@cindex help, where to find

If you need help installing, using or changing Octave, the mailing list

@example
help-octave@@che.utexas.edu
@end example

exists for the discussion of Octave matters related to using,
installing, and porting Octave.  If you would like to join the
discussion, please send a short note to

@example
help-octave-request@@che.utexas.edu
            ^^^^^^^
@end example

@strong{Please do not} send requests to be added or removed from the the
mailing list, or other administrative trivia to the list itself.
