Known Causes of Trouble with Octave
***********************************

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.

Actual Bugs We Haven't Fixed Yet
================================

  * Recursive function calls are not currently allowed.

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.

  * Problems with finite and isinf on systems that don't have isinf() but do have finite().

     The copy of math.h supplied with libg++ version 2.3 (and possibly other versions as well) declares finite() as

          double finite (double);

     even though some (many? all?) systems declare it as

          int finite (double);

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

  * 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 libg++/config/rs6000.mh and re-run make install for libg++.

          *** 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

  * 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.

  * 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

          Stanford University

          Office of Technology Licensing

          857 Serra Street

          Stanford CA 94305-6225

          Tel: (415) 723-0651

          Fax: (415) 725-7295

     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.

Disappointments and Misunderstandings
=====================================

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

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.  See 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.

Have You Found a Bug?
=====================

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

  * If Octave gets a fatal signal, for any input whatever, that is a bug.  Reliable interpreters never crash.

  * If Octave produces incorrect results, for any input whatever, that is a bug.

  * 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.

  * If Octave produces an error message for valid input, that is a bug.

  * 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''.

      suggestions

  * If you are an experienced user of programs like Octave, your suggestions for improvement are welcome in any case.

Where to Report Bugs
====================

Send bug reports for Octave to:

     bug-octave@che.utexas.edu

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

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

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

How to Report Bugs
==================

The fundamental principle of reporting bugs usefully is this: 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:

  * The version of Octave.  You can get this by noting the version number that is printed when Octave starts, or running it with the -v option.

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

  * 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.

  * 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.

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

  * The command-line arguments you gave to the configure command when you installed the interpreter.

  * 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.

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

  * 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.

  * 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.

  * 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.

Here are some things that are not necessary:

  * 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 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.

  * 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.

  * 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.

Sending Patches for Octave
==========================

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.

  * 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.)

  * 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.

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

  * Don't mix together changes made for different reasons. Send them 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.

  * 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.

  * Use 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 -c format.

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

  * 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 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.

  * 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 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.

How To Get Help with Octave
===========================

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

     help-octave@che.utexas.edu

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

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

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