Summary of important user-visible changes for version 4.2:
---------------------------------------------------------

 ** The parser has been extended to accept, but ignore, underscore
    characters in numbers.  This facilitates writing more legible code
    by using '_' as a thousands separator or to group nibbles into bytes
    in hex constants.

    Examples: 1_000_000 == 1e6 or 0xDE_AD_BE_EF

 ** The parser has been extended to understand binary numbers which
    begin with the prefix '0b' or '0B'.  The value returned is Octave's
    default numeric class of double, not at unsigned integer class.
    Therefore numbers greater than flintmax, i.e., 2^53, will lose some
    precision.

    Examples: 0b101 == 5 or 0B1100_0001 == 0xC1

 ** The default colormap is now set to "viridis" which is also the
    default colormap in matplotlib.  This new colormap fixes some of the
    main issues with the old default colormap "jet" such as its bad
    "luminance profile" and is also more similar to Matlab's new default
    colormap "parula".

 ** Octal ('\NNN') and hex ('\xNN') escape sequences in single quoted
    strings are now interpreted by the function do_string_escapes().
    The *printf family of functions now supports octal and hex escape
    sequences in single-quoted strings for Matlab compatibility.

 ** Special octal and hex escape sequences for the pattern and
    replacement strings in regular expressions are now interpreted for
    Matlab compatibility.

    octal: '\oNNN' or '\o{NNN}'
    hex  : '\xNN'  or '\x{NN}'

 ** Unknown escape sequences in the replacement string for regexprep are
    now substituted with their unescaped version and no warning is
    emitted.  This change was made for Matlab compatibility.

    Example: regexprep ('a', 'a', 'x\yz')
             => 'xyz'

 ** mkfifo now interprets the MODE argument as an octal, not decimal,
    integer.  This is consistent with the equivalent shell command.

 ** linspace now returns an empty matrix if the number of requested
    points is 0 or a negative number.  This change was made to be
    compatible with Matlab releases newer than 2011.  In addition,
    Octave no longer supports matrix inputs for A or B.

 ** The griddata function no longer plots the interpolated mesh if no
    output argument is requested, instead the vector or array of
    interpolated values is always returned for Matlab compatibility.

 ** The surfnorm function now returns unnormalized (magnitude != 1)
    normal vectors for compatibility with Matlab.

 ** The quadl function now uses an absolute, rather than relative,
    tolerance for Matlab compatibility.  The default tolerance is 1e-6
    which may result in lower precision results than previous versions
    of Octave which used eps as the relative tolerance.  The quadl
    function has also been extended to return a second output with the
    total number of function evaluations.

 ** Other new functions added in 4.2:

      deg2rad
      evalc
      hash
      im2double
      psi
      odeset
      odeget
      ode45
      rad2deg

 ** Deprecated functions.

    The following functions have been deprecated in Octave 4.2 and will
    be removed from Octave 4.6 (or whatever version is the second major
    release after 4.2):

      Function             | Replacement
      ---------------------|------------------
      bitmax               | flintmax
      mahalanobis          | mahal in Octave-Forge statistics pkg
      md5sum               | hash
      sleep                | pause
      usleep               | pause
      wavread              | audioread
      wavwrite             | audiowrite

 ** The following functions were deprecated in Octave 3.8 and have been
    removed from Octave 4.2.

      default_save_options    java_new
      gen_doc_cache           java_unsigned_conversion
      interp1q                javafields
      isequalwithequalnans    javamethods
      java_convert_matrix     re_read_readline_init_file
      java_debug              read_readline_init_file
      java_invoke             saving_history

 ** The global error_state variable in Octave's C++ API has been
    deprecated and will be removed in a future version.  Now the error
    and print_usage functions throw an exception
    (octave_execution_exception) after displaying the error message.
    This makes the error and print_usage functions in C++ work more like
    the corresponding functions in the scripting language.

 ** The default error handlers in liboctave have been updated to use
    exceptions.  After displaying an error message they no longer return
    control to the calling program.  The error handler function can be
    customized through the global variables
    "current_liboctave_error_handler" and
    "current_liboctave_error_with_id_handler".  If a programmer has
    installed their own custom error handling routines when directly
    linking with liboctave then these must be updated to throw an
    exception and not return to the calling program.

 ** The system for common errors and warnings has been renamed from
    gripe_XXX to either err_XXX if error is called or warn_XXX if
    warning is called.  The gripe_XXX functions are deprecated and will
    be removed in version 4.6.

 ** New configure option, --enable-address-sanitizer-flags, to build
    Octave with memory allocator checks (similar to those in valgrind)
    built in.

Summary of important user-visible changes for version 4.0:
---------------------------------------------------------

 ** A graphical user interface is now the default when running Octave
    interactively.  The start-up option --no-gui will run the familiar
    command line interface, and still allows use of the GUI dialogs and
    qt plotting toolkit.  The option --no-gui-libs runs a minimalist
    command line interface that does not link with the Qt libraries and
    uses the fltk toolkit for plotting.

 ** Octave now uses OpenGL graphics with Qt widgets by default.  If
    OpenGL libraries are not available when Octave is built, gnuplot is
    used.  You may choose to use the fltk or gnuplot toolkit for
    graphics by executing the command

      graphics_toolkit ("fltk")
        OR
      graphics_toolkit ("gnuplot")

    Adding such a command to your ~/.octaverc file will set the default
    for each session.

 ** A new syntax for object oriented programming termed classdef has
    been introduced.  See the manual for more extensive documentation of
    the classdef interface.

    New keywords:

      classdef      endclassdef
      enumeration   endenumeration
      events        endevents
      methods       endmethods
      properties    endproperties

 ** New audio functions and classes:

      audiodevinfo  audioread      sound
      audioinfo     audiorecorder  soundsc
      audioplayer   audiowrite

 ** Other new classes in Octave 4.0:

      audioplayer    inputParser
      audiorecorder

 ** Optional stricter Matlab compatibility for ranges, diagonal
    matrices, and permutation matrices.

    Octave has internal optimizations which use space-efficient storage
    for the three data types above.  Three new functions have been added
    which control whether the optimizations are used (default), or
    whether the data types are stored as full matrices.

    disable_range   disable_diagonal_matrix   disable_permutation_matrix

    All three optimizations are disabled if Octave is started with the
    --braindead command line option.

 ** The preference

      do_braindead_shortcircuit_evaluation

    is now enabled by default.

 ** The preference

      allow_noninteger_range_as_index

    is now enabled by default and the warning ID

      Octave:noninteger-range-as-index

    is now set to "on" by default instead of "error" by default and "on"
    for --traditional.

 ** The "backtrace" warning option is now enabled by default.  This
    change was made for Matlab compatibility.

 ** For compatibility with Matlab, the "ismatrix (x)" function now only
    checks the dimension of "x".  The old behaviour of "ismatrix" is
    obtained by "isnumeric (x) || islogical (x) || ischar (x)".

 ** The nextpow2 function behaviour has been changed for vector inputs.
    Instead of computing `nextpow2 (length (x))', it will now compute
    nextpow2 for each element of the input.  This change is Matlab
    compatible, and also prevents bugs for "vectors" of length 1.

 ** polyeig now returns a row vector of eigenvalues rather than a matrix
    with the eigenvalues on the diagonal.  This change was made for
    Matlab compatibility.

 ** Interpolation function changes for Matlab compatibility

    The interpolation method 'cubic' is now equivalent to 'pchip' for
    interp1, interp2, and interp3.  Previously, 'cubic' was equivalent
    to 'spline' for interp2.  This may produce different results as
    'spline' has continuous 1st and 2nd derivatives while 'pchip' only
    has a continuous 1st derivative.  The methods 'next' and 'previous'
    have been added to interp1 for compatibility.

 ** The delaunay function has been extended to accept 3-D inputs for
    Matlab compatibility.  The delaunay function no longer plots the
    triangulation if no output argument is requested, instead, the
    triangulation is always returned.  The delaunay3 function which
    handles 3-D inputs has been deprecated in favor of delaunay.

 ** The trigonometric functions asin and acos return different phase
    values from previous versions of Octave when the input is outside
    the principal branch ([-1, 1]).  If the real portion of the input is
    greater than 1 then the limit from below is taken.  If the real
    portion is less than 1 then the limit from above is taken.  This
    criteria is consistent with several other numerical analysis
    software packages.

 ** The hyperbolic function acosh now returns values with a phase in the
    range [-pi/2, +pi/2].  Previously Octave returned values in the
    range [0, pi].  This is consistent with several other numerical
    analysis software packages.

 ** strfind changes when using empty pattern ("") for Matlab
    compatibility

    strfind now returns an empty array when the pattern itself is empty.
    In previous versions of Octave, strfind matched at every character
    location when the pattern was empty.

      NEW
      strfind ("abc", "") => []
      OLD
      strfind ("abc", "") => [1, 2, 3, 4]

 ** Integer formats used in the printf family of functions now work for
    64-bit integers and are more compatible with Matlab when printing
    non-integer values.  Now instead of truncating, Octave will switch
    the effective format to '%g' in the following circumstances:

      * the value of an integer type (int8, uint32, etc.) value exceeds
        the maximum for the format specifier.  For '%d', the limit is
        intmax ('int64') and for '%u' it is intmax ('uint64').

      * round(x) != x or the value is outside the range allowed by the
        integer format specifier.

    There is still one difference: Matlab switches to '%e' and Octave
    switches to '%g'.

 ** The functions intersect, setdiff, setxor, and union now return a
    column vector as output unless the input was a row vector.  This
    change was made for Matlab compatibility.

 ** The inpolygon function now returns true for points that are within
    the polygon OR on it's edge.  This change was made for Matlab
    compatibility.

 ** The archive family of functions (bzip2, gzip, zip, tar) and their
    unpacking routines (bunzip2, gunzip, unzip, untar, unpack) have been
    recoded.  Excepting unpack, the default is now to place files in the
    same directory as the archive (on unpack) or as the original files
    (on archiving).

 ** Qt and FLTK graphics toolkits now support offscreen rendering on
    Linux.  In other words, print will work even when the figure
    visibility is "off".

 ** Z-order stacking issues with patches, grid lines, and line object
    plot markers for on screen display and printing have all been
    resolved.  For 2-D plots the axis grid lines can be placed on top of
    the plot with set (gca, "layer", "top").

 ** The patch graphic object has been overhauled.  It now produces
    visual results equivalent to Matlab even for esoteric combinations
    of faces/vertices/cdata.

 ** The polar() plot function now draws a circular theta axis and radial
    rho axis rather than using a rectangular x/y axis.

 ** linkprop has been completely re-coded for performance and Matlab
    compatibility.  It now returns a linkprop object which must be
    stored in a variable for as long as the graphic objects should
    remain linked.  To unlink properties use 'clear hlink' where hlink
    is the variable containing the linkprop object.

 ** isprime has been extended to operate on negative and complex inputs.

 ** xor has been extended to accept more than two arguments in which
    case it performs cumulative XOR reduction.

 ** The following functions now support N-dimensional arrays:

      fliplr   flipud   rot90   rectint

 ** The new warning ID "Octave:data-file-in-path" replaces the three
    previous separate warning IDs "Octave:fopen-file-in-path",
    "Octave:load-file-in-path", and "Octave:md5sum-file-in-path".

 ** The warning ID Octave:singular-matrix-div has been replaced by
    Octave:nearly-singular-matrix and Octave:singular-matrix.

 ** The warning ID Octave:matlab-incompatible has been replaced by
    Octave:language-extension to better reflect its meaning.

 ** The warning ID Octave:broadcast has been removed.  Instead automatic
    broadcasting will throw an Octave:language-extension warning.  This
    warning ID is used for broadcasting as well as other features not
    available in Matlab.

 ** Other new functions added in 4.0:

      annotation
      bandwidth
      cubehelix
      dir_in_loadpath
      flip
      frame2im
      get_home_directory
      hgload
      hgsave
      ichol
      ilu
      im2frame
      isbanded
      isdiag
      isstudent
      istril
      istriu
      javachk
      jit_failcnt
      linkaxes
      lscov
      metaclass
      numfields
      open
      ordschur
      pan
      qmr
      rotate
      rotate3d
      sylvester
      unsetenv
      validateattributes
      zoom

 ** inline() scheduled for eventual deprecation by Matlab

    Functions created through the use of inline are scheduled for
    deprecation by Matlab.  When this occurs Octave will continue to
    support inline functions for an indeterminate amount of time before
    also removing support.  All new code should use anonymous functions
    in place of inline functions.

 ** Deprecated functions.

    The following functions have been deprecated in Octave 4.0 and will
    be removed from Octave 4.4 (or whatever version is the second major
    release after 4.0):

      Function             | Replacement
      ---------------------|------------------
      bicubic              | interp2
      delaunay3            | delaunay
      dump_prefs           | individual preference get/set routines
      find_dir_in_path     | dir_in_loadpath
      finite               | isfinite
      fmod                 | rem
      fnmatch              | glob or regexp
      gmap40               | ----
      loadaudio            | audioread
      luinc                | ilu or ichol
      mouse_wheel_zoom     | mousewheelzoom axes property
      nfields              | numfields
      octave_tmp_file_name | tempname
      playaudio            | audioplayer
      saveaudio            | audiowrite
      syl                  | sylvester
      usage                | print_usage

      allow_noninteger_range_as_index
      do_braindead_shortcircuit_evaluation
      setaudio

 ** The following functions were deprecated in Octave 3.8 and will be
    removed from Octave 4.2 (or whatever version is the second major
    release after 3.8):

      default_save_options    java_new
      gen_doc_cache           java_unsigned_conversion
      interp1q                javafields
      isequalwithequalnans    javamethods
      java_convert_matrix     re_read_readline_init_file
      java_debug              read_readline_init_file
      java_invoke             saving_history

 ** The following functions were deprecated in Octave 3.6 and have been
    removed from Octave 4.0.

      cut                polyderiv
      cor                shell_cmd
      corrcoef           studentize
      __error_text__     sylvester_matrix
      error_text

 ** The following keywords were deprecated in Octave 3.8 and have been
    removed from Octave 4.0

      static

 ** The following configuration variables were deprecated in Octave 3.8
    and have been removed from Octave 4.0

      CC_VERSION  (now GCC_VERSION)
      CXX_VERSION (now GXX_VERSION)

 ** The internal function atan2 of the sparse matrix class has been
    deprecated in Octave 4.0 and will be removed from Octave 4.4 (or
    whatever version is the second major release after 4.0).  Use the
    Fatan2 function with sparse inputs as a replacement.

 ** The internal class Octave_map was deprecated in Octave 3.8 and has
    been removed from Octave 4.0.  Replacement classes are octave_map
    (struct array) or octave_scalar_map for a single structure.

 ** The configure option --enable-octave-allocator has been removed.
    The internal class octave_allocator declared in oct-alloc.h has been
    removed.  The header remains, but is deprecated.  The macros to
    access the class (DECLARE_OCTAVE_ALLOCATOR, DEFINE_OCTAVE_ALLOCATOR,
    and DEFINE_OCTAVE_ALLOCATOR2) are now unconditionally defined to be
    empty.

 ** Octave now has OpenMP enabled by default if the system provides a
    working OpenMP implementation.  This allows oct-file modules to take
    advantage of OpenMP if desired.  This can be disabled when building
    Octave with the configure option --disable-openmp.

 ** Octave now automatically truncates intermediate calculations done
    with floating point values to 64 bits.  Some hardware math
    co-processors, such as the x87, maintain extra precision, but this
    leads to disagreements in calculations when compared to reference
    implementations in software using the IEEE standard for double
    precision.  There was no measurable performance impact to this
    change, but it may be disabled with the configure option
    --disable-float-truncate.  MinGW and Cygwin platforms, as well as
    GCC compilers >= 5.0 require this feature.  Non-x87 hardware, or
    hardware using SSE options exclusively, can disable float truncation
    if desired.

---------------------------------------------------------

See NEWS.3 for old news.