# Projects

The list below summarizes features or bug fixes we would like to see in Octave. if you start working steadily on a project, please let octave-maintainers@octave.org know. We might have information that could help you. You should also read the Contributing Guidelines.

This list is not exclusive -- there are many other things that might be good projects, but it might instead be something we already have. Also, some of the following items may not actually be considered good ideas now. So please check with octave-maintainers@octave.org before you start working on some large project.

Summer of Code students, please also see SoC Project Ideas.

If you're looking for small project, something more suited to start getting involved with Octave development or to fill a boring evening, see short projects

# Numerical

• Improve complex mapper functions. See W. Kahan, Branch Cuts for Complex Elementary Functions, or Much Ado About Nothing's Sign Bit (in The State of the Art in Numerical Analysis, eds. Iserles and Powell, Clarendon Press, Oxford, 1987) for explicit trigonometric formulae.
• Make functions like gamma() return the right IEEE Inf or NaN values for extreme args or other undefined cases.
• Improve sqp.
• Fix CollocWt? to handle Laguerre polynomials. Make it easy to extend it to other polynomial types.
• Add optional arguments to colloc so that it's not restricted to Legendre polynomials.
• Move rand, eye, xpow, xdiv, etc., functions to the matrix classes.
• Improve design of ODE, DAE, classes.
• Make QR more memory efficient for large matrices when not all the columns of Q are required (apparently this is not handled by the lapack code yet).
• Evaluate harmonics and cross-correlations of unevenly sampled and nonstationary time series, as in http://www.jstatsoft.org/v11/i02 (which has C code with interface to R). (This is now partly implemented in the lssa package.)

## General purpose Finite Element library

Octave-Forge already has a set of packages for discretizing Partial Differential operators by Finite Elements and/or Finite Volumes, namely the bim package which relies on the msh package (which is in turn based on gmsh) for creating and managing 2D triangular and 3D tetrahedral meshes and on the fpl package for visualizing 2D results within Octave or exporting 2D or 3D results in a format compatible with Paraview or VisIT. These packages, though, offer only a limited choice of spatial discretization methods which are based on low degree polynomials and therefore have a low order of accuracy even for problems with extremely smooth solutions. The GeoPDEs project, on the other hand, offers a complete suite of functions for discretizing a wide range of differential operators related to important physical problems and uses basis functions of arbitrary polynomial degree that allow the construction of methods of high accuracy. These latter, though, are based on the IsoGeometric Analysis Method which, although very powerful and often better performing, is less widely known and adopted than the Finite Elements Method. The implementation of a general purpose library of Finite Elements seems therefore a valuable addition to Octave-Forge. Two possible interesting choices for implementing this package exist, the first consists of implementing the most common Finite Element spaces in the GeoPDEs framework, which is possible as IsoGeometric Analysis can be viewed as a superset of the Finite Element Method, the other is to construct Octave language bindings for the free software library FEniCS based on the existing C++ or Python interfaces. This second approach has been developed during the GSOC 2013 and the Octave-Forge package fem-fenics is now available. However, fem-fenics could be extended in many different ways:

• implement the bindings for the UFL language inside Octave
• add new functions already available with Fenics but not yet in Octave
• create new functions specifically suited for Octave
• improve the efficiency of the code

The main goal for the fem-fenics package is ultimately to be merged with the FEnics project itself, so that it can remain in-sync with the main library development.

## Implement solver for initial-boundary value problems for parabolic-elliptic PDEs in 1D

The project will deliver a solver for initial-boundary value problems for parabolic-elliptic PDEs in 1D similar to Matlab's function pdepe. A good starting point is the method of lines for which you can find more details here and here, whereas an example implementation can be found here. In addition, this page provides some useful material.

## Implement solver for 1D nonlinear boundary value problems

The project will complete the implementation of the bvp4c solver that is already available in an initial version in the odepkg package by adding a proper error estimator and will implement a matlab-compatible version of the bvp5c solver. Details on the methods to be implemented can be found in this paper on bvp4c and this paper on bvp5c. Further details are available in this book.

## Geometric integrators for Hamiltonian Systems

Geometric (AKA Symplectic) integrators are useful for multi-dimensional classical mechanics problems and for molecular dynamics simulations. The odepkg package has a number of solvers for ODE, DAE and DDE problems but none of them is currently specifically suited for second order problems in general and Hamiltonian systems in particular. Therefore a new package for geometric integrators would be a useful contribution. This could be created as new package or added as a set of new functions for odepkg. The function interface should be consistent throughout the package and should be modeled to follow that of other functions in odepkg (or that of DASPK and LSODE) but will need specific extensions to accommodate for specific options that only make sense for this specific class of solvers. An initial list of methods to be implemented includes (but is not limited to)

• Symplectic Euler methods, see here and here
• Störmer-Verlet method, see here and here
• Velocity Verlet method, see here and here
• Symplectic partitioned Runge-Kutta methods, see here or here
• Spectral Variational Integrator methods, see here or here

For this latter there is an existing code which is already working but needs to be improved, posted on the patch tracker. Furthermore, methods to implement solutions of problems with rigid constraints should be implemented, e.g.

## Matlab-compatible ODE solvers in core-Octave

• Adapt "odeset" and "odeget" from the odepkg package so that the list of supported options is more Matlab-compatible, in the sense that all option names that are supported by Matlab should be available. On the other hand, Matlab returns an error if an option which is not in the list of known options is passed to "odeset", but we would rather make this a warning in order to allow for special extensions, for example for symplectic integrators.
• Adapt the interface of "ode45" in odepkg to be completely Matlab compatible, fix its code and documentation style and move it to Octave-core.
• Build Matlab compatible versions of "ode15s" and "ode15i". jwe has prototype implementations here of these built as wrappers to "dassl" and "daspk". An initial approach could be to just improve these wrappers, but eventually it would be better to have wrappers for "IDA" from the sundials library.
• Implement Matlab compatible versions of "deval".

## High Precision Arithmetic Computation

The architecture consists of an Octave class interface implementing "mp" (multi-precision) objects. Arithmetic operations are forwarded to MPL using MEX files. This is totally transparent to the end user, except when displaying numbers. This implementation needs to be ported and tested under Octave.

# GUI/IDE

• Søren Hauberg has suggested that we need C++ code that can:
• Determine if a line of code could be fully parsed, i.e. it would return true for "plot (x, y);", but false for "while (true)".
• Evaluate a line of code and return the output as a string (it would be best if it could provide three strings: output, warnings and errors).
• Query defined variables, i.e. get a list of currently defined variables. Bonus points if it could tell you if anything had changed since the last time you checked the variables (could also be done with signals).
• Create a better (G)UI for the profiler. This may be done with Qt, but not necessarily.

## Sisotool. Create a graphical design tool for tuning closed loop control system (Control package)

When tuning a SISO feedback system it is very helpful to be able to grab a pole or a zero and move them by dragging them with the mouse. As they are moving the software must update all the plotted lines. There should be the ability to display various graphs rlocuse, bode, step, impulse etc. and have them all change dynamically as the mouse is moving. The parameters of the compensator must be displayed and updated. Recently, some implementation was done during GSoC 2018, see https://eriveltongualter.github.io/GSoC2018/final.html for details.

# Sparse Matrices

The paper by Bateman & Adler is good reading for understanding the sparse matrix implementation.

• Improve QR factorization functions, using idea based on CSPARSE cs_dmsol.m
• Improve QR factorization by replacing CXSPARSE code with SPQR code, and make the linear solve return 2-norm solutions for ill-conditioned matrices based on this new code
• Sparse logical indexing in idx_vector class so that something like a = sprandn (1e6, 1e6, 1e-6); a(a<1) = 0; won't cause a memory overflow.
• Other missing Functions
• lsqr
• minres
• symmlq

# Strings

• Consider making octave_print_internal() print some sort of text representation for unprintable characters instead of sending them directly to the terminal. (But don't do this for fprintf!)
• Consider changing the default value of string_fill_char' from SPC to NUL.

# Other Data Types

• Template functions for mixed-type ops.
• Convert other functions for use with the floating point type including quad, dasrt, daspk, etc.

# Input/Output

• Make fread and fwrite work for complex data. Iostreams based versions of these functions would also be nice, and if you are working on them, it would be good to support other size specifications (integer*2, etc.).
• Move some pr-output stuff to liboctave.
• Make the cutoff point for changing to packed storage a user-preference variable with default value 8192.
• Complain if there is not enough disk space available (I think there is simply not enough error checking in the code that handles writing data).
• Make it possible to tie arbitrary input and output streams together, similar to the way iostreams can be tied together.
• Expand imwrite options. This shouldn't be too hard to implement, since it's wrapped around GraphicsMagick.
• Extend Octave functions to work on stored arrays that are too big to fit in RAM, similar to available R packages.

# Interpreter

The interpreter is written in C++, undocumented. There are many possible projects associated with it.

Required skills: Very good C and C++ knowledge, possibly also understanding of GNU bison and flex. Understanding how compilers and interpreters are made plus being able to understand how to use a profiler and a debugger will probably be essential skills.

• Allow customization of the debug prompt.
• Fix the parser so that
  if (expr) 'this is a string' end


is parsed as IF expr STRING END. (see this post on the mailing list)

• Clean up functions in input.cc that handle user input (there currently seems to be some unnecessary duplication of code and it seems overly complex).
• Consider allowing an arbitrary property list to be attached to any variable. This could be a more general way to handle the help string that can currently be added with document'.
• Allow more command line options to be accessible as built-in variables (--echo-commands, etc.).
• Make the interpreter run faster.
• Allow arbitrary lower bounds for array indexing.
• Improve performance of recursive function calls.
• Improve the way ignore_function_time_stamp works to allow selecting by individual directories or functions.
• Add a command-line option to tell Octave to just do syntax checking and not execute statements.
• Clean up symtab and variable stuff.
• Input stream class for parser files -- must manage buffers for flex and context for global variable settings.
• make parser do more semantic checking, continue after errors when compiling functions, etc.
• Make LEXICAL_ERROR have a value that is the error message for parse_error() to print?
• Add a run-time alias mechanism that would allow things like alias fun function_with_a_very_long_name so that function_with_a_very_long_name' could be invoked as fun'.
• Allow local changes to variables to be written more compactly than is currently possible with unwind_protect. For example,
      function f ()
local prefer_column_vectors = something;
...
endfunction



would be equivalent to

       function f ()
save_prefer_column_vectors = prefer_column_vectors;
unwind_protect
prefer_column_vectors = something;
...
unwind_protect_cleanup
prefer_column_vectors = save_prefer_column_vectors;
end_unwind_protect
endfunction


• Fix all function files to check for bogus inputs (wrong number or types of input arguments, wrong number of output arguments).
• Handle options for built-in functions more consistently.
• Too much time is spent allocating and freeing memory. What can be done to improve performance?
 Use move constructors rather than copy constructors for things like dim_vectors which are repeatedly created just to initialize Array or Matrix objects.

• Error output from Fortran code is ugly. Something should be done to make it look better.
• It would be nice if output from the Fortran routines could be passed through the pager.
• Attempt to recognize common subexpressions in the parser.
• Consider making it possible to specify an empty matrix with a syntax like [](e1, e2). Of course at least one of the expressions must be zero...
• Is Matrix::fortran_vec() really necessary?
• Rewrite whos and the symbol_record_info class. Write a built-in function that gives all the basic information, then write who and whos as M-files.
• On systems that support matherr(), make it possible for users to enable the printing of warning messages.
• Make it possible to mark variables and functions as read-only.
• Make it possible to write a function that gets a reference to a matrix in memory and change one or more elements without generating a second copy of the data.
• Use nanosleep instead of usleep if it is available? Apparently nanosleep is to be preferred over usleep on Solaris systems.

## Improve JIT compiling

Octave's interpreter is very slow on some loops. Recently, thanks to Max Brister's work, an initial implementation of a just-in-time compiler (JITC) in LLVM for GSoC 2012. This project consists in understanding Max's current implementation and extending it so that functions and exponents (e.g. 2^z) compile with the JITC. This requires knowledge of compilers, C++, LLVM, and the Octave or Matlab languages. A capable student who demonstrates the ability to acquire this knowledge quickly may also be considered. Max himself will mentor this project. Here is Max's OctConf 2012 presentation about his current implementation. See also JIT.

## Improve memory management

From profiling the interpreter, it appears that a lot of time is spending allocating and deallocating memory. A better memory management algorithm might provide some improvement.

## Implement classdef classes

Matlab has two kinds of classes: old style @classes and new style classdef. Octave has only fully implemented the old style. There is partial support for classdef classes in version 4.0, refer to the classdef status page for what is not yet implemented. There is irregular work here, and classdef is a very complicated thing to fully implement. A successful project would be to implement enough of classdef for most basic usages. Familiarity with Matlab's current classdef support would be a huge plus. Michael Goffioul and jwe can mentor this.

Although there's already a substantial classdef support in current octave code base, there are still many areas that are unimplemented or need improvements. The main ones that come to my mind are:

• support for events
• support for enums
• support for "import" (this requires good understanding of octave internals, especially the symbol table)
• improving multiple inheritance and method resolution
• honoring and computing "Sealed" attribute
• support for function handle to methods

## Improve MPI package

Octave Forge's MPI package is a wrapper for basic MPI functions for parallel computing. It is implemented by wrapping MPI function calls in simple DLD functions that map Octave's Datataypes to MPI Derived Datatypes. The proposed project deals with improving and extending the Octave MPI package, for example:

• Octave MPI applications can currently be only run in batch mode, add the ability to launch parallel jobs and collect their output in an interactive Octave session.
• Implement functions for non-blocking communication (MPI_Isend, MPI_Irecv)
• Implement one-to-many (Broadcast, Scatter), many-to-one (Reduce, Gather), and many-to-many (All Reduce, Allgather) communication routines

# Graphics

• Correctly handle case where DISPLAY is unset. Provide --no-window-system or --nodisplay (?) option. Provide --display=DISPLAY option? How will this work with gnuplot (i.e., how do we know whether gnuplot requires an X display to display graphics)?
• Implement transparency and lighting in OpenGL backend(s). A basic implementation was available in JHandles. This needs to be ported/re-implement/re-engineered/optimized in the C++ OpenGL renderer of octave.
• Implement a Cairo-based renderer for 2D-only graphics, with support for PS/PDF/SVG output (for printing).
• On 'imagesc' plots, report the matrix values also based on the mouse position, updating on mouse moving.
• Add data cursor to trace data values in figure.

## Lighting

Implement transparency and lighting in OpenGL backend(s). A basic implementation is available in JHandles. This needs to be ported/re-implement/re-engineered/optimized in the C++ OpenGL renderer of Octave.

## Object selection in OpenGL renderer

This project is about the implementation of a selection method of graphics elements within the OpenGL renderer [1]

## Non-OpenGL renderer

Besides the original gnuplot backend, Octave also contains an OpenGL-based renderer for advanced and more powerful 3D plots. However, OpenGL is not perfectly suited for 2D-only plots where other methods could result in better graphics. The purpose of this project is to implement an alternate graphics renderer for 2D only plots (although 3D is definitely not the focus, extending the new graphics renderer to support basic 3D features should also be taken into account). There is no particular toolkit/library that must be used, but natural candidates are:

• Qt: the GUI is currently written in Qt and work is also in progress to provide a Qt/OpenGL based backend [2]
• Cairo: this library is widely used and known to provides high-quality graphics with support for PS/PDF/SVG output.

## TeX/LaTeX markup

Text objects in plots (like titles, labels, texts...) in the OpenGL renderer only support plain text mode without any formatting possibility. Support for TeX and/or LaTeX formatting needs to be added.

• The TeX formatting support actually only consists of a very limited subset of the TeX language. This can be implemented directly in C++ into Octave by extending the existing text engine, avoiding to add a dependency on a full TeX system. Essentially, support for Greek letters, super/sub-scripts, and several mathematical symbols needs to be supported. For example,
\alpha \approx \beta_0 + \gamma^\chi
Would be rendered as,
α ≈ β0 + γχ
This is analogous to how special characters may be included in a wiki using html.
&alpha; &asymp; &beta;<sub>0</sub> + &gamma;<sup>&chi;</sup>
The text object's extent for the rendered result needs to be calculated and the text placed the location specified by the text object's position property. An itemized list of a text objects properties can be found here.
• On the other hand, the LaTeX formatting support is expected to provide full LaTeX capabilities. This will require to use an external LaTeX system to produce text graphics in some format (to be specified) that is then integrated into Octave plots.
The matplotlib project has already done this in Python and might be used as an example of how to do this in Octave. Mediawiki has also also done something similar. There is also JLaTeXMath, a Java API to display LaTeX code in mathematical mode.

# History

• Add an option to allow saving input from script files in the history list.
• The history command should accept two numeric arguments to indicate a range of history entries to display, save or read.
• Avoid writing the history file if the history list has not changed.
• Avoid permission errors if the history file cannot be opened for writing.
• Fix history problems — core dump if multiple processes are writing to the same history file?

# Configuration and Installation

• Makefile changes:
• eliminate for loops
• define shell commands or eliminate them
• consolidate targets
• Create a docs-only distribution?
• Convert build system to a non-recursive Automake setup. See how Makefile.am files currently include module.mk files in subdirectories, extend this concept to the entire project so there is only one top-level Makefile.am. Done, except for special dir libgnu which is the only SUBDIRS listed in configure.ac.

# Documentation and On-Line Help

• Improve the Texinfo Documentation for the interpreter. It would be useful to have lots more examples, to not have so many forward references, and to not have very many simple lists of functions.
• Doxygen documentation for the C++ classes.
• Make index entries more consistent to improve behavior of help -i.
• Make help -i try to find a whole word match first.
• Flesh out this wiki

# Tests

• Improved set of tests: [3]
• Tests for various functions. Would be nice to have a test file corresponding to every function (see below)
• Tests for element by element operators: + - .* ./ .\ .^ | & < <= == >= > != !
• Tests for boolean operators: && ||
• Tests for other operators: * / \ ' .'
• Tests from bug reports.
• Tests for indexed assignment. Need to consider the following:
• fortran-style indexing
• zero-one indexing
• assignment of empty matrix as well as values resizing
• Tests for all internal functions.
• Implement a coverage tool for collecting coverage data and generating code coverage reports on m-file functions and scripts. This would be very useful for Octave development as well as for users who want a code coverage report for their own functions and scripts.

We are far from even having one test for every function, so focus should be on getting the breadth of coverage first before trying to get the depth of 100% statement coverage. As of Dec 2015, 202 of 1020 m-files have no tests. Some of these will be plotting functions which have demos instead, but that leaves enough functions to be an interesting project. As of Dec 2015, there are 485 instances of C++ functions which need tests.

After Octave is compiled, running the make check build target will run the full test suite and generate a file called test/fntests.log in the build directory with a summary of the results. At the end of the file is a list of all functions for which no tests were found. An extract is posted in the files missing tests page. If you are not building Octave yourself, the test suite can be run on an installed binary copy by executing the __run_test_suite__ command at the Octave prompt. The fntests.log file will be written in the current directory in this case.

There also need to be tests for functions written in the C++ files. See Add_BIST_tests_for_octave_functions_written_in_C++ for instructions and a list of instances.

# Programming

• Better error messages for missing operators?
• Eliminate duplicate enums in pt-exp.cc, pt-const.cc, and ov.cc.
• Handle octave_print_internal() stuff at the liboctave level. Then the octave_value classes could just call on the print() methods for the underlying classes.
• As much as possible, eliminate explicit checks for the types of octave_value objects so that user-defined types will automatically do the right thing in more cases.
• Only include config.h in files that actually need it, instead of including it in every .cc file. Unfortunately, this might not be so easy to figure out.
• GNU coding standards:
• Add a Makefile' target to the Makefiles.
• Comments on #else and #endif preprocessor commands.
• Change error message format to match standards everywhere.
• Eliminate more global variables.
• Move procstream to liboctave.
• Use references and classes in more places.
• Share more code among the various _options functions.
• Reduce the amount of datatypes in liboctave.

# Miscellaneous

• Implement some functions for interprocess communication: bind, accept, connect, gethostbyname, etc. (This functionality is already available in the octave sockets package, what is the purpose of moving it to core octave?)
• The ability to transparently handle very large files: Juhana K Kouhia <kouhia@nic.funet.fi> wrote:
If I have a one-dimensional signal data with the size 400 Mbytes, then what are my choices to operate with it:
• I have to split the data
• Octave has a virtual memory on its own and I don't have to worry about the splitting.
If I split the data, then my easily programmed processing programs will become hard to program.
If possible, I would like to have the virtual memory system in Octave i.e., the all big files, the user see as one big array or such. There could be several user selectable models to do the virtual memory depending on what kind of data the user have (1d, 2d) and in what order they are processed (stream or random access).
• An interface to gdb. Michael Smolsky <fnsiguc@weizmann.weizmann.ac.il> wrote:
I was thinking about a tool, which could be very useful for me in my numerical simulation work. It is an interconnection between gdb and octave. We are often managing very large arrays of data in our fortran or c codes, which might be studied with the help of octave at the algorithm development stages. Assume you're coding, say, wave equation. And want to debug the code. It would be great to pick some array from the memory of the code you're developing, fft it and see the image as a log-log plot of the spectral density. I'm facing similar problems now. To avoid high c-development cost, I develop in matlab/octave, and then rewrite into c. It might be so much easier, if I could off-load a c array right from the debugger into octave, study it, and, perhaps, change some [many] values with a convenient matlab/octave syntax, similar to a(:,51:250)=zeros(100,200), and then store it back into the memory of my c code.
• Implement gdb extensions for Octave types. Octave has the etc/gdbinit file, which has some basic support for displaying the contents of Octave types. Add more extensions to make it easier to debug octave_values and other Octave types.
• Spatial statistics, including covariogram estimation and kriging -- perhaps via an interface to gstat?
• the units function from the miscellaneous package works by parsing the output of from a call to GNU units. This can be made much more robust by writing it in C++ and including its library "units.h"

# Marketing and Community

• Make it easier for newcomers to contribute.

## Improve Windows binary packaging

We are currently able to build and provide a installer for Windows. The build process involves cross-compiling on a Linux system using a fork of the MXE project to build Octave and all of its dependencies. Any ideas for improving this process to make it easier or faster, or to improve the installer itself or the installation experience for Windows users would be appreciated.

Skills Required: Knowledge of GNU build systems, Makefiles, configure files, chasing library dependencies, how to use a compiler. No m-scripting or C++ necessary, beyond understanding the C++ compilation model.

## Improve macOS binary packaging

We would like to be able to easily generate binary packages for macOS. Right now, it's difficult and tedious to do so. Most OS X users install Octave using one of the source-based package managers such as Homebrew or MacPorts. Any way to help us build a binary package would be appreciated. Required knowledge is understanding how building binaries in macOS works. Our current approach to building binaries for Windows is to cross-compile from a GNU system using MXE, something similar may be possible for OS X (GUB?).

Skills Required: Knowledge of GNU build systems, Makefiles, configure files, chasing library dependencies, how to use a compiler. If you choose to work on GUB, Python will be required. No m-scripting or C++ necessary, beyond understanding the C++ compilation model.

# Performance

• A profiler for Octave would be a very useful tool. And now we have one! But it really needs a better interface.
• Having parfor functioning would speed code development and execution now that multicore architectures are widespread. See here and here. Existing code from the parallel and mpi packages could perhaps be adapted for this.

# Packaging

• create a system that allows packages to deprecate functions as in core. Possibilities are:
• get pkg to accept a deprecated directory inside the package and add it to the search path. Functions in those directories would have to be treated the same as the ones inside the core deprecated
• PKG_ADD can be used to hack this. Package developers would still have to actually write the warnings on the function code but this would allow to have the functions in a separate directory so they don't foget to remove them on the next release
• the package developer can also use something like Make to create a normal package from something that actually had a more complex structure, inclusive deprecated directories
• allow to download and install multiple versions of the same package
• make the package just a bit more verbose by default (specifics?)
• make pkg a little more like apt-get (what specific features of apt-get is this referring to?)
• make pkg support more than one src directory
• subdirectories with makefiles and top level make command of: cd <subdir> && \${MAKE}... ok as a substitute?
• make pkg able to supply extra configure and make flags, useful for distributions, including -j for make (pkg now passes --jobs=N automatically, CFLAGS and CXXFLAGS environment variables are already respected, what's missing?)

# Preferences

Octave has several functions for managing user preferences. Many function use persistent variables instead of relying upon the preference features.

• The function edit () contains a persistent structure used as its personal set of preferences. These can all be moved to the user preference group for the editor.
• "EDITOR"
• "HOME"
• "AUTHOR"
• "EMAIL"
• "MODE"
• "EDITINPLACE"
• The savepath () function modifies the startup script (rcfile), ~/.octaverc and inserts commands to allow the next session to begin with the same path. Instead user preference can be created for startup items and a preference for the user specified path can be added. Perhaps two path preferences should be used. One for the elements that should precede the core path and those that should follow. A start up directory preference might also be added to allow the user to specify where Octave should begin the next session.
• "PREPATH"
• "POSTPATH"
• "STARTUPDIR"
• A preference group for plotting can also be added. A preference for the default terminal would be useful for those who want to override the default. Preferences for the default graphicstoolkit can also be added.
• GNUPLOTTERM
• GRAPHICSTOOLKIT
• A preference group for printing can include preferences for the default printer, the ghostscript command, and possibly other parameters like orientation, and resolution.
• PRINTER
• GHOSTSCRIPTCOMMAND
• ORIENTATION
• RESOLUTION
• Searching the m-files for use of persistent` should turn up other opportunities to use preferences.

# Bugs

There are always bugs to fix. The bug tracker is a good place to find tasks needing a hand. See also Short projects#Bugs.

# Matlab compatibility

## Missing functions

There are certain functions present in MATLAB known to be missing in Octave.

One list is provided on the source for function __unimplemented.m__, subfunction missing_functions; it can be edited in the Octave GUI or browsed at [4].

Lists are also kept for several packages.

It is also possible to look at existing FOSS implementations, from FreeMat and Scilab (for more closely compatible languages) to R or Scipy or Julia (for less compatible versions). Obviously, it is NOT OK to look at the Matlab implementation since this is not free software!

## Functions under different name

Many Octave Forge functions perform the same as functions from matlab packages. However, they often exist under a different name or have incompatible API's. Often fixing this is a matter of changing their names, swap the order of their input arguments. At least, a list of this functions would be helpful.