This is Info file octave, produced by Makeinfo-1.64 from the input file
octave.tex.

START-INFO-DIR-ENTRY
* Octave: (octave).	Interactive language for numerical computations.
END-INFO-DIR-ENTRY

   Copyright (C) 1996, 1997 John W. Eaton.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.


File: octave,  Node: Signal Processing,  Next: Image Processing,  Prev: Control Theory,  Up: Top

Signal Processing
*****************

   I hope that someday Octave will include more signal processing
functions.  If you would like to help improve Octave in this area,
please contact (bug-octave@bevo.che.wisc.edu).

 - Function File:  detrend (X, P)
     If X is a vector, `detrend (X, P)' removes the  best fit of a
     polynomial of order P from the data X.

     If X is a matrix, `detrend (X, P)' does the same  for each column
     in X.

     The second argument is optional.  If it is not specified, a value
     of 1  is assumed.  This corresponds to removing a linear trend.

 - Loadable Function:  fft (A, N)
     Compute the FFT of A using subroutines from FFTPACK.  If A is a
     matrix, `fft' computes the FFT for each column of A.

     If called with two arguments, N is expected to be an integer
     specifying the number of elements of A to use.  If A is a matrix,
     N specifies the number of rows of A to use.  If N is larger than
     the size of A, A is resized and padded with zeros.

 - Loadable Function:  ifft (A, N)
     Compute the inverse FFT of A using subroutines from FFTPACK.  If A
     is a matrix, `fft' computes the inverse FFT for each column of A.

     If called with two arguments, N is expected to be an integer
     specifying the number of elements of A to use.  If A is a matrix,
     N specifies the number of rows of A to use.  If N is larger than
     the size of A, A is resized and padded with zeros.

 - Loadable Function:  fft2 (A, N, M)
     Compute the two dimensional FFT of A.

     The optional arguments N and M may be used specify the number of
     rows and columns of A to use.  If either of these is larger than
     the size of A, A is resized and padded with zeros.

 - Loadable Function:  ifft2 (A, N, M)
     Compute the two dimensional inverse FFT of A.

     The optional arguments N and M may be used specify the number of
     rows and columns of A to use.  If either of these is larger than
     the size of A, A is resized and padded with zeros.

 - Function File:  fftconv (A, B, N)
     Return the convolution of the vectors A and B, as a vector  with
     length equal to the `length (a) + length (b) - 1'.  If A  and B
     are the coefficient vectors of two polynomials, the returned
     value is the coefficient vector of the product polynomial.

     The computation uses the FFT by calling the function `fftfilt'.  If
     the optional argument N is specified, an N-point FFT is used.

 - Function File:  fftfilt (B, X, N)
     With two arguments, `fftfilt' filters X with the FIR filter B
     using the FFT.

     Given the optional third argument, N, `fftfilt' uses the
     overlap-add method to filter X with B using an N-point FFT.

 - Loadable Function: y = filter (B, A, X)
 - Loadable Function: [Y, SF] = filter (B, A, X, SI)
     Return the solution to the following linear, time-invariant
     difference equation:

             N                   M
            SUM a(k+1) y(n-k) = SUM b(k+1) x(n-k)      for 1<=n<=length(x)
            k=0                 k=0

     where  N=length(a)-1 and M=length(b)-1.  An equivalent form of
     this equation is:

                      N                   M
            y(n) = - SUM c(k+1) y(n-k) + SUM d(k+1) x(n-k)  for 1<=n<=length(x)
                     k=1                 k=0

     where  c = a/a(1) and d = b/a(1).

     If the fourth argument SI is provided, it is taken as the initial
     state of the system and the final state is returned as SF.  The
     state vector is a column vector whose length is equal to the
     length of the longest coefficient vector minus one.  If SI is not
     supplied, the initial state vector is set to all zeros.

     In terms of the z-transform, y is the result of passing the
     discrete- time signal x through a system characterized by the
     following rational system function:

                       M
                      SUM d(k+1) z^(-k)
                      k=0
            H(z) = ----------------------
                         N
                    1 + SUM c(k+1) z(-k)
                        k=1

 - Function File: [H, W] = freqz (B, A, N, "whole")
     Return the complex frequency response H of the rational IIR filter
     whose numerator and denominator coefficients are B and A,
     respectively.  The response is evaluated at N angular frequencies
     between 0 and   2*pi.

     The output value W is a vector of the frequencies.

     If the fourth argument is omitted, the response is evaluated at
     frequencies between 0 and   pi.

     If N is omitted, a value of 512 is assumed.

     If A is omitted, the denominator is assumed to be 1 (this
     corresponds to a simple FIR filter).

     For fastest computation, N should factor into a small number of
     small primes.

 - Function File:  sinc (X)
     Return   sin(pi*x)/(pi*x).

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File: octave,  Node: Image Processing,  Next: Audio Processing,  Prev: Signal Processing,  Up: Top

Image Processing
****************

   Octave can display images with the X Window System using the
`xloadimage' program.  You do not need to be running X in order to
manipulate images, however, so some of these functions may be useful
even if you are not able to view the results.

   Loading images only works with Octave's image format (a file with a
matrix containing the image data, and a matrix containing the
colormap).  Contributions of robust, well-written functions to read
other image formats are welcome.  If you can provide them, or would like
to improve Octave's image processing capabilities in other ways, please
contact (bug-octave@bevo.che.wisc.edu).

 - Function File:  colormap (MAP)
 - Function File:  colormap ("default")
     Set the current colormap.

     `colormap (MAP)' sets the current colormap to MAP.  The  color map
     should be an N row by 3 column matrix.  The columns  contain red,
     green, and blue intensities respectively.  All entries  should be
     between 0 and 1 inclusive.  The new colormap is returned.

     `colormap ("default")' restores the default colormap (a gray scale
     colormap with 64 entries).  The default colormap is returned.

     With no arguments, `colormap' returns the current color map.

 - Function File:  gray (N)
     Return a gray colormap with N entries corresponding to values from
     0 to N-1.  The argument N should be a scalar.  If it is  omitted,
     64 is assumed.

 - Function File: [IMG, MAP] = gray2ind ()
     Convert a gray scale intensity image to an Octave indexed image.

 - Function File:  image (X, ZOOM)
     Display a matrix as a color image.  The elements of X are indices
     into the current colormap and should have values between 1 and the
     length of the colormap.  If ZOOM is omitted, a value of 4 is
     assumed.

 - Function File:  imagesc (X, ZOOM)
     Display a scaled version of the matrix X as a color image.  The
     matrix is scaled so that its entries are indices into the current
     colormap.  The scaled matrix is returned.  If ZOOM is omitted, a
     value of 4 is assumed.

 - Function File:  imshow (X, MAP)
 - Function File:  imshow (X, N)
 - Function File:  imshow (I, N)
 - Function File:  imshow (R, G, B)
     Display images.

     `imshow (X)' displays an indexed image using the current  colormap.

     `imshow (X, MAP)' displays an indexed image using the  specified
     colormap.

     `imshow (I, N)' displays a gray scale intensity image.

     `imshow (R, G, B)' displays an RGB image.

 - Function File:  ind2gray (X, MAP)
     Convert an Octave indexed image to a gray scale intensity image.
     If MAP is omitted, the current colormap is used to determine the
     intensities.

 - Function File: [R, G, B] = ind2rgb (X, MAP)
     Convert an indexed image to red, green, and blue color components.
     If MAP is omitted, the current colormap is used for the
     conversion.

 - Function File: [X, MAP] = loadimage (FILE)
     Load an image file and it's associated color map from the specified
     FILE.  The image must be stored in Octave's image format.

 - Function File:  rgb2ntsc (RGB)
     Image format conversion.

 - Function File:  ntsc2rgb (YIQ)
     Image format conversion.

 - Function File:  ocean (N)
     Create color colormap.  The argument N should be a scalar.  If it
     is omitted, 64 is assumed.

 - Function File: [X, MAP] = rgb2ind (R, G, B)
     Convert and RGB image to an Octave indexed image.

 - Function File:  saveimage (FILE, X, FMT, MAP)
     Save the matrix X to FILE in image format FMT.  Valid  values for
     FMT are

    `"img"'
          Octave's image format.  The current colormap is also saved in
          the file.

    `"ppm"'
          Portable pixmap format.

    `"ps"'
          PostScript format.  Note that images saved in PostScript
          format can not  be read back into Octave with loadimage.

     If the fourth argument is supplied, the specified colormap will
     also be  saved along with the image.

     Note: if the colormap contains only two entries and these entries
     are  black and white, the bitmap ppm and PostScript formats are
     used.  If the  image is a gray scale image (the entries within
     each row of the colormap  are equal) the gray scale ppm and
     PostScript image formats are used,  otherwise the full color
     formats are used.

 - Built-in Variable: IMAGEPATH
     A colon separated list of directories in which to search for image
     files.

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File: octave,  Node: Audio Processing,  Next: System Utilities,  Prev: Image Processing,  Up: Top

Audio Processing
****************

   Octave provides a few functions for dealing with audio data.  An
audio `sample' is a single output value from an A/D converter, i.e., a
small integer number (usually 8 or 16 bits), and audio data is just a
series of such samples.  It can be characterized by three parameters:
the sampling rate (measured in samples per second or Hz, e.g. 8000 or
44100), the number of bits per sample (e.g. 8 or 16), and the number of
channels (1 for mono, 2 for stereo, etc.).

   There are many different formats for representing such data.
Currently, only the two most popular, *linear encoding* and *mu-law
encoding*, are supported by Octave.  There is an excellent FAQ on audio
formats by Guido van Rossum <guido@cwi.nl> which can be found at any
FAQ ftp site, in particular in the directory
`/pub/usenet/news.answers/audio-fmts' of the archive site
`rtfm.mit.edu'.

   Octave simply treats audio data as vectors of samples (non-mono data
are not supported yet).  It is assumed that audio files using linear
encoding have one of the extensions `lin' or `raw', and that files
holding data in mu-law encoding end in `au', `mu', or `snd'.

 - Function File:  lin2mu (X)
     If the vector X represents mono audio data in 8- or 16-bit  linear
     encoding, `lin2mu (X)' is the corresponding mu-law  encoding.

 - Function File:  mu2lin (X, BPS)
     If the vector X represents mono audio data in mu-law encoding,
     `mu2lin' converts it to linear encoding.  The optional argument
     BPS specifies whether the input data uses 8 bit per sample
     (default) or 16 bit.

 - Function File:  loadaudio (NAME, EXT, BPS)
     Loads audio data from the file `NAME.EXT' into the  vector X.

     The extension EXT determines how the data in the audio file is
     interpreted;  the extensions `lin' (default) and `raw'  correspond
     to linear, the extensions `au', `mu', or `snd'  to mu-law encoding.

     The argument BPS can be either 8 (default) or 16, and specifies
     the number of bits per sample used in the audio file.

 - Function File:  saveaudio (NAME, X, EXT, BPS)
     Saves a vector X of audio data to the file `NAME.EXT'.  The
     optional parameters EXT and BPS determine the encoding and the
     number of bits per sample used  in the audio file (see
     `loadaudio');  defaults are `lin' and  8, respectively.

   The following functions for audio I/O require special A/D hardware
and operating system support.  It is assumed that audio data in linear
encoding can be played and recorded by reading from and writing to
`/dev/dsp', and that similarly `/dev/audio' is used for mu-law
encoding.  These file names are system-dependent.  Improvements so that
these functions will work without modification on a wide variety of
hardware are welcome.

 - Function File:  playaudio (NAME, EXT)
 - Function File:  playaudio (X)
     Plays the audio file `NAME.EXT' or the audio data  stored in the
     vector X.

 - Function File:  record (SEC, SAMPLING_RATE)
     Records SEC seconds of audio input into the vector X.  The
     default value for SAMPLING_RATE is 8000 samples per second, or
     8kHz.  The program waits until the user types RET and then
     immediately starts to record.

   usage: setaudio ([w_type [, value]])

   executes the shell command `mixer [w_type [, value]]'

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File: octave,  Node: System Utilities,  Next: Tips,  Prev: Audio Processing,  Up: Top

System Utilities
****************

   This chapter describes the functions that are available to allow you
to get information about what is happening outside of Octave, while it
is still running, and use this information in your program.  For
example, you can get information about environment variables, the
current time, and even start other programs from the Octave prompt.

* Menu:

* Timing Utilities::
* Filesystem Utilities::
* Controlling Subprocesses::
* Process ID Information::
* Environment Variables::
* Current Working Directory::
* Password Database Functions::
* Group Database Functions::
* System Information::


File: octave,  Node: Timing Utilities,  Next: Filesystem Utilities,  Prev: System Utilities,  Up: System Utilities

Timing Utilities
================

   Octave's core set of functions for manipulating time values are
patterned after the corresponding functions from the standard C library.
Several of these functions use a data structure for time that includes
the following elements:

`usec'
     Microseconds after the second (0-999999).

`sec'
     Seconds after the minute (0-61).  This number can be 61 to account
     for leap seconds.

`min'
     Minutes after the hour (0-59).

`hour'
     Hours since midnight (0-23).

`mday'
     Day of the month (1-31).

`mon'
     Months since January (0-11).

`year'
     Years since 1900.

`wday'
     Days since Sunday (0-6).

`yday'
     Days since January 1 (0-365).

`isdst'
     Daylight Savings Time flag.

`zone'
     Time zone.

In the descriptions of the following functions, this structure is
referred to as a TM_STRUCT.

 - Loadable Function:  time ()
     Return the current time as the number of seconds since the epoch.
     The epoch is referenced to 00:00:00 CUT (Coordinated Universal
     Time) 1 Jan 1970.  For example, on Monday February 17, 1997 at
     07:15:06 CUT, the value returned by `time' was 856163706.

 - Function File:  ctime (T)
     Convert a value returned from `time' (or any other nonnegative
     integer), to the local time and return a string of the same form as
     `asctime'.  The function `ctime (time)' is equivalent to `asctime
     (localtime (time))'.  For example,

           ctime (time ())
          => "Mon Feb 17 01:15:06 1997"

 - Loadable Function:  gmtime (T)
     Given a value returned from time (or any nonnegative integer),
     return a time structure corresponding to CUT.  For example,

          gmtime (time ())
               => {
                     usec = 0
                     year = 97
                     mon = 1
                     mday = 17
                     sec = 6
                     zone = CST
                     min = 15
                     wday = 1
                     hour = 7
                     isdst = 0
                     yday = 47
                   }

 - Loadable Function:  localtime (T)
     Given a value returned from time (or any nonnegative integer),
     return a time structure corresponding to the local time zone.

          localtime (time ())
               => {
                     usec = 0
                     year = 97
                     mon = 1
                     mday = 17
                     sec = 6
                     zone = CST
                     min = 15
                     wday = 1
                     hour = 1
                     isdst = 0
                     yday = 47
                   }

 - Loadable Function:  mktime (TM_STRUCT)
     Convert a time structure corresponding to the local time to the
     number of seconds since the epoch.  For example,

          mktime (localtime (time ())
               => 856163706

 - Function File:  asctime (TM_STRUCT)
     Convert a time structure to a string using the following five-field
     format: Thu Mar 28 08:40:14 1996.  For example,

           asctime (localtime (time ())
          => "Mon Feb 17 01:15:06 1997\n"

     This is equivalent to `ctime (time ())'.

 - Loadable Function:  strftime (TM_STRUCT)
     Format a time structure in a flexible way using `%' substitutions
     similar to those in `printf'.  Except where noted, substituted
     fields have a fixed size; numeric fields are padded if necessary.
     Padding is with zeros by default; for fields that display a single
     number, padding can be changed or inhibited by following the `%'
     with one of the modifiers described below.  Unknown field
     specifiers are copied as normal characters.  All other characters
     are copied to the output without change.  For example,

          strftime ("%r (%Z) %A %e %B %Y", localtime (time ())
               => "01:15:06 AM (CST) Monday 17 February 1997"

     Octave's `strftime' function supports a superset of the ANSI C
     field specifiers.

     Literal character fields:

    `%'
          % character.

    `n'
          Newline character.

    `t'
          Tab character.

     Numeric modifiers (a nonstandard extension):

    `- (dash)'
          Do not pad the field.

    `_ (underscore)'
          Pad the field with spaces.

     Time fields:

    `%H'
          Hour (00-23).

    `%I'
          Hour (01-12).

    `%k'
          Hour (0-23).

    `%l'
          Hour (1-12).

    `%M'
          Minute (00-59).

    `%p'
          Locale's AM or PM.

    `%r'
          Time, 12-hour (hh:mm:ss [AP]M).

    `%R'
          Time, 24-hour (hh:mm).

    `%s'
          Time in seconds since 00:00:00, Jan 1, 1970 (a nonstandard
          extension).

    `%S'
          Second (00-61).

    `%T'
          Time, 24-hour (hh:mm:ss).

    `%X'
          Locale's time representation (%H:%M:%S).

    `%Z'
          Time zone (EDT), or nothing if no time zone is determinable.

     Date fields:

    `%a'
          Locale's abbreviated weekday name (Sun-Sat).

    `%A'
          Locale's full weekday name, variable length (Sunday-Saturday).

    `%b'
          Locale's abbreviated month name (Jan-Dec).

    `%B'
          Locale's full month name, variable length (January-December).

    `%c'
          Locale's date and time (Sat Nov 04 12:02:33 EST 1989).

    `%C'
          Century (00-99).

    `%d'
          Day of month (01-31).

    `%e'
          Day of month ( 1-31).

    `%D'
          Date (mm/dd/yy).

    `%h'
          Same as %b.

    `%j'
          Day of year (001-366).

    `%m'
          Month (01-12).

    `%U'
          Week number of year with Sunday as first day of week (00-53).

    `%w'
          Day of week (0-6).

    `%W'
          Week number of year with Monday as first day of week (00-53).

    `%x'
          Locale's date representation (mm/dd/yy).

    `%y'
          Last two digits of year (00-99).

    `%Y'
          Year (1970-).

   Most of the remaining functions described in this section are not
patterned after the standard C library.  Some are available for
compatiblity with MATLAB and others are provided because they are
useful.

 - Function File:  clock ()
     Return a vector containing the current year, month (1-12), day
     (1-31),  hour (0-23), minute (0-59) and second (0-61).  For
     example,

           clock ()
          => [ 1993, 8, 20, 4, 56, 1 ]

     The function clock is more accurate on systems that have the
     `gettimeofday' function.

 - Function File:  date ()
     Return the date as a character string in the form DD-MMM-YY.  For
     example,

           date ()
          => "20-Aug-93"

 - Function File:  etime (T1, T2)
     Return the difference (in seconds) between two time values
     returned from `clock'.  For example:

           t0 = clock ();
           # many computations later...
           elapsed_time = etime (clock (), t0);

     will set the variable `elapsed_time' to the number of seconds since
     the variable `t0' was set.

 - Function File: [TOTAL, USER, SYSTEM] = cputime ();
     Return the CPU time used by your Octave session.  The first output
     is  the total time spent executing your process and is equal to
     the sum of  second and third outputs, which are the number of CPU
     seconds spent  executing in user mode and the number of CPU
     seconds spent executing in  system mode, respectively.  If your
     system does not have a way to report  CPU time usage, `cputime'
     returns 0 for each of its output values.   Note that because
     Octave used some CPU time to start, it is reasonable  to check to
     see if `cputime' works by checking to see if the total  CPU time
     used is nonzero.

 - Function File:  is_leap_year (YEAR)
     Return 1 if the given year is a leap year and 0 otherwise.  If no
     arguments are provided, `is_leap_year' will use the current year.
     For example,

           is_leap_year (2000)
          => 1

 - Function File:  tic ()
 - Function File:  toc ()
     These functions set and check a wall-clock timer.  For example,

           tic ();
           # many computations later...
           elapsed_time = toc ();

     will set the variable `elapsed_time' to the number of seconds since
     the most recent call to the function `tic'.

     If you are more interested in the CPU time that your process used,
     you  should use the `cputime' function instead.  The `tic' and
     `toc' functions report the actual wall clock time that elapsed
     between the calls.  This may include time spent processing other
     jobs or  doing nothing at all.  For example,

           tic (); sleep (5); toc ()
          => 5
           t = cputime (); sleep (5); cputime () - t
          => 0

     (This example also illustrates that the CPU timer may have a fairly
     coarse resolution.)

 - Built-in Function:  pause (SECONDS)
     Suspend the execution of the program.  If invoked without any
     arguments, Octave waits until you type a character.  With a
     numeric argument, it pauses for the given number of seconds.  For
     example, the following statement prints a message and then waits 5
     seconds before clearing the screen.

          fprintf (stderr, "wait please...
          ");
          pause (5);
          clc;

 - Built-in Function:  sleep (SECONDS)
     Suspend the execution of the program for the given number of
     seconds.

 - Built-in Function:  usleep (MICROSECONDS)
     Suspend the execution of the program for the given number of
     microseconds.  On systems where it is not possible to sleep for
     periods of time less than one second, `usleep' will pause the
     execution for `round (MICROSECONDS / 1e6)' seconds.


File: octave,  Node: Filesystem Utilities,  Next: Controlling Subprocesses,  Prev: Timing Utilities,  Up: System Utilities

Filesystem Utilities
====================

   Octave includes the following functions for renaming and deleting
files, creating, deleting, and reading directories, and for getting
information about the status of files.

 - Built-in Function: [ERR, MSG] = rename (OLD, NEW)
     Change the name of file OLD to NEW.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [ERR, MSG] = unlink (FILE)
     Delete the file named FILE.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [FILES, ERR, MSG] = readdir (DIR)
     Return names of the files in the directory DIR as an array of
     strings.  If an error occurs, return an empty matrix in FILES.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [ERR, MSG] = mkdir (DIR)\nCreate a directory
          named DIR.
     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [ERR, MSG] = rmdir (DIR)
     Remove the directory named DIR.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [ERR, MSG] = mkfifo (NAME)
     Create a FIFO special file named NAME with file mode MODE \n If
     successful, ERR is 0 and MSG is an empty string.  Otherwise, ERR
     is nonzero and MSG contains a system-dependent error message.

 - Built-in Function:  umask (MASK)
     Set the permission mask for file creation.  The parameter MASK  is
     an integer, interpreted as an octal number.  If successful,
     returns the previous value of the mask (as an integer to be
     interpreted as an octal number); otherwise an error message is
     printed.

 - Built-in Function: [INFO, ERR, MSG] = stat (FILE)
 - Built-in Function: [INFO, ERR, MSG] = lstat (FILE)
     Return a structure S containing the following information about
     FILE.

    `dev'
          ID of device containing a directory entry for this file.

    `ino'
          File number of the file.

    `modestr'
          File mode, as a string of ten letters or dashes as would be
          returned by `ls -l'.

    `nlink'
          Number of links.

    `uid'
          User ID of file's owner.

    `gid'
          Group ID of file's group.

    `rdev'
          ID of device for block or character special files.

    `size'
          Size in bytes.

    `atime'
          Time of last access in the same form as time values returned
          from `time'.  *Note Timing Utilities::.

    `mtime'
          Time of last modification in the same form as time values
          returned from `time'.  *Note Timing Utilities::.

    `ctime'
          Time of last file status change in the same form as time
          values returned from `time'.  *Note Timing Utilities::.

    `blksize'
          Size of blocks in the file.

    `blocks'
          Number of blocks allocated for file.

     If the call is successful ERR is 0 and MSG is an empty string.  If
     the file does not exist, or some other error occurs, S is an empty
     matrix, ERR is -1, and MSG contains the corresponding system error
     message.

     If FILE is a symbolic link, `stat' will return information about
     the actual file the is referenced by the link.  Use `lstat' if you
     want information about the symbolic link itself.

     For example,

          [s, err, msg] = stat ("/vmlinuz")
                => s =
                  {
                    atime = 855399756
                    rdev = 0
                    ctime = 847219094
                    uid = 0
                    size = 389218
                    blksize = 4096
                    mtime = 847219094
                    gid = 6
                    nlink = 1
                    blocks = 768
                    modestr = -rw-r--r--
                    ino = 9316
                    dev = 2049
                  }
               => err = 0
               => msg =

 - Built-in Function:  glob (PATTERN)
     Given an array of strings in PATTERN, return the list of file
     names that any of them, or an empty string if no patterns match.
     Tilde expansion is performed on each of the patterns before
     looking for matching file names.  For example,

          glob ("/vm*")
               => "/vmlinuz"

     Note that multiple values are returned in a string matrix with the
     fill character set to ASCII NUL.

 - Built-in Function:  file_in_path (PATH, FILE)
     Return the absolute name name of FILE if it can be found in PATH.
     The value of PATH should be a colon-separated list of directories
     in the format described for the built-in variable `LOADPATH'.

     If the file cannot be found in the path, an empty matrix is
     returned.  For example,

          file_in_path (LOADPATH, "nargchk.m")
               => "/share/octave/2.0/m/general/nargchk.m"

 - Built-in Function:  tilde_expand (STRING)
     Performs tilde expansion on STRING.  If STRING begins with a tilde
     character, (`~'), all of the characters preceding the first slash
     (or all characters, if there is no slash) are treated as a
     possible user name, and the tilde and the following characters up
     to the slash are replaced by the home directory of the named user.
     If the tilde is followed immediately by a slash, the tilde is
     replaced by the home directory of the user running Octave.  For
     example,

          tilde_expand ("~joeuser/bin")
               => "/home/joeuser/bin"
          tilde_expand ("~/bin")
               => "/home/jwe/bin"


File: octave,  Node: Controlling Subprocesses,  Next: Process ID Information,  Prev: Filesystem Utilities,  Up: System Utilities

Controlling Subprocesses
========================

   Octave includes some high-level commands like `system' and `popen'
for starting subprocesses.  If you want to run another program to
perform some task and then look at its output, you will probably want
to use these functions.

   Octave also provides several very low-level Unix-like functions which
can also be used for starting subprocesses, but you should probably only
use them if you can't find any way to do what you need with the
higher-level functions.

 - Built-in Function:  system (STRING, RETURN_OUTPUT, TYPE)
     Execute a shell command specified by STRING.  The second argument
     is optional.  If TYPE is `"async"', the process is started in the
     background and the process id of the child process is returned
     immediately.  Otherwise, the process is started, and Octave waits
     until it exits.  If TYPE argument is omitted, a value of `"sync"'
     is assumed.

     If two input arguments are given (the actual value of
     RETURN_OUTPUT is irrelevant) and the subprocess is started
     synchronously, or if SYSTEM is called with one input argument and
     one or more output arguments, the output from the command is
     returned.  Otherwise, if the subprocess is executed synchronously,
     it's output is sent to the standard output.  To send the output of
     a command executed with SYSTEM through the pager, use a command
     like

          disp (system (cmd, 1));

     or

          printf ("%s
          ", system (cmd, 1));

     The `system' function can return two values.  The first is any
     output from the command that was written to the standard output
     stream, and the second is the output status of the command.  For
     example,

          [output, status] = system ("echo foo; exit 2");

     will set the variable `output' to the string `foo', and the
     variable `status' to the integer `2'.

 - Built-in Function: fid = popen (COMMAND, MODE)
     Start a process and create a pipe.  The name of the command to run
     is given by COMMAND.  The file identifier corresponding to the
     input or output stream of the process is returned in FID.  The
     argument MODE may be

    `"r"'
          The pipe will be connected to the standard output of the
          process, and open for reading.

    `"w"'
          The pipe will be connected to the standard input of the
          process, and open for writing.

     For example,

          fid = popen ("ls -ltr / | tail -3", "r");
          while (isstr (s = fgets (fid)))
            fputs (stdout, s);
          endwhile
               -| drwxr-xr-x  33 root  root  3072 Feb 15 13:28 etc
               -| drwxr-xr-x   3 root  root  1024 Feb 15 13:28 lib
               -| drwxrwxrwt  15 root  root  2048 Feb 17 14:53 tmp

 - Built-in Function:  pclose (FID)
     Close a file identifier that was opened by `popen'.  You may also
     use `fclose' for the same purpose.

 - Function File: [IN, OUT, PID] = popen2 (COMMAND, ARGS)
     Start a subprocess with two-way communication.  The name of the
     process  is given by COMMAND, and ARGS is an array of strings
     containing options for the command.  The file identifiers for the
     input  and output streams of the subprocess are returned in IN and
     OUT.  If execution of the command is successful, PID  contains the
     process ID of the subprocess.  Otherwise, PID is -1.

     For example,

           [in, out, pid] = popen2 ("sort", "-nr");
           fputs (in, "these\nare\nsome\nstrings\n");
           fclose (in);
           while (isstr (s = fgets (out)))
             fputs (stdout, s);
           endwhile
           fclose (out);
          -| are
          -| some
          -| strings
          -| these

 - Built-in Variable: EXEC_PATH
     The variable `EXEC_PATH' is a colon separated list of directories
     to search when executing subprograms.  Its initial value is taken
     from the environment variable `OCTAVE_EXEC_PATH' (if it exists) or
     `PATH', but that value can be overridden by the command line
     argument `--exec-path PATH', or by setting the value of
     `EXEC_PATH' in a startup script.  If the value of `EXEC_PATH'
     begins (ends) with a colon, the directories

          OCTAVE-HOME/libexec/octave/site/exec/ARCH
          OCTAVE-HOME/libexec/octave/VERSION/exec/ARCH

     are prepended (appended) to `EXEC_PATH', where OCTAVE-HOME is the
     top-level directory where all of Octave is installed (the default
     value is `').  If you don't specify a value for `EXEC_PATH'
     explicitly, these special directories are prepended to your shell
     path.

   In most cases, the following functions simply decode their arguments
and make the corresponding Unix system calls.  For a complete example
of how they can be used, look at the definition of the function
`popen2'.

 - Built-in Function: [PID, MSG] = fork ()
     Create a copy of the current process.

     Fork can return one of the following values:

    > 0
          You are in the parent process.  The value returned from
          `fork' is the process id of the child process.  You should
          probably arrange to wait for any child processes to exit.

    0
          You are in the child process.  You can call `exec' to start
          another process.  If that fails, you should probably call
          `exit'.

    < 0
          The call to `fork' failed for some reason.  You must take
          evasive action.  A system dependent error message will be
          waiting in MSG.

 - Built-in Function: [ERR, MSG] = exec (FILE, ARGS)
     Replace current process with a new process.  Calling `exec' without
     first calling `fork' will terminate your current Octave process and
     replace it with the program named by FILE.  For example,

          exec ("ls" "-l")

     will run `ls' and return you to your shell prompt.

     If successful, `exec' does not return.  If `exec' does return, ERR
     will be nonzero, and MSG will contain a system-dependent error
     message.

 - Built-in Function: [FILE_IDS, ERR, MSG] = pipe ()
     Create a pipe and return the vector FILE_IDS, which corresponding
     to the reading and writing ends of the pipe.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.

 - Built-in Function: [FID, MSG] = dup2 (OLD, NEW)
     Duplicate a file descriptor.

     If successful, FID is greater than zero and contains the new file
     ID.  Otherwise, FID is negative and MSG contains a
     system-dependent error message.

 - Built-in Function: [PID, MSG] = waitpid (PID, OPTIONS)
     Wait for process PID to terminate.  The PID argument can be:

    -1
          Wait for any child process.

    0
          Wait for any child process whose process group ID is equal to
          that of the Octave interpreter process.

    > 0
          Wait for termination of the child process with ID PID.

     The OPTIONS argument can be:

    0
          Wait until signal is received or a child process exits (this
          is the default if the OPTIONS argument is missing).

    1
          Do not hang if status is not immediately available.

    2
          Report the status of any child processes that are stopped,
          and whose status has not yet been reported since they stopped.

    3
          Implies both 1 and 2.

     If the returned value of PID is greater than 0, it is the process
     ID of the child process that exited.  If an error occurs, PID will
     be less than zero and MSG will contain a system-dependent error
     message.

 - Built-in Function: [ERR, MSG] = fcntl (FID, REQUEST, ARG)
     Change the properties of the open file FID.  The following values
     may be passed as REQUEST:

    `F_DUPFD'
          Return a duplicate file descriptor.

    `F_GETFD'
          Return the file descriptor flags for FID.

    `F_SETFD'
          Set the file descriptor flags for FID.

    `F_GETFL'
          Return the file status flags for FID.  The following codes
          may be returned (some of the flags may be undefined on some
          systems).

         `O_RDONLY'
               Open for reading only.

         `O_WRONLY'
               Open for writing only.

         `O_RDWR'
               Open for reading and writing.

         `O_APPEND'
               Append on each write.

         `O_NONBLOCK'
               Nonblocking mode.

         `O_SYNC'
               Wait for writes to complete.

         `O_ASYNC'
               Asynchronous I/O.

    `F_SETFL'
          Set the file status flags for FID to the value specified by
          ARG.  The only flags that can be changed are `O_APPEND' and
          `O_NONBLOCK'.

     If successful, ERR is 0 and MSG is an empty string.  Otherwise,
     ERR is nonzero and MSG contains a system-dependent error message.


File: octave,  Node: Process ID Information,  Next: Environment Variables,  Prev: Controlling Subprocesses,  Up: System Utilities

Process, Group, and User IDs
============================

 - Built-in Function: pgid = getpgrp ()
     Return the process group id of the current process.

 - Built-in Function: pid = getpid ()
     Return the process id of the current process.

 - Built-in Function: pid = getppid ()
     Return the process id of the parent process.

 - Built-in Function: euid = geteuid ()
     Return the effective user id of the current process.

 - Built-in Function: uid = getuid ()
     Return the real user id of the current process.

 - Built-in Function: egid = getegid ()
     Return the effective group id of the current process.

 - Built-in Function: gid = getgid ()
     Return the real group id of the current process.


File: octave,  Node: Environment Variables,  Next: Current Working Directory,  Prev: Process ID Information,  Up: System Utilities

Environment Variables
=====================

 - Built-in Function:  getenv (VAR)
     Return the value of the environment variable VAR.  For example,

          getenv ("PATH")

     returns a string containing the value of your path.

 - Built-in Function:  putenv (VAR, VALUE)
     Set the value of the environment variable VAR to VALUE.


File: octave,  Node: Current Working Directory,  Next: Password Database Functions,  Prev: Environment Variables,  Up: System Utilities

Current Working Directory
=========================

 - Command: cd DIR
 - Command: chdir DIR
     Change the current working directory to DIR.  If DIR is omitted,
     the current directory is changed to the users home directory.  For
     example,

          cd ~/octave

     Changes the current working directory to `~/octave'.  If the
     directory does not exist, an error message is printed and the
     working directory is not changed.

 - Command: ls OPTIONS
 - Command: dir OPTIONS
     List directory contents.  For example,

          ls -l
               -| total 12
               -| -rw-r--r--   1 jwe  users  4488 Aug 19 04:02 foo.m
               -| -rw-r--r--   1 jwe  users  1315 Aug 17 23:14 bar.m

     The `dir' and `ls' commands are implemented by calling your
     system's directory listing command, so the available options may
     vary from system to system.

 - Built-in Function:  pwd ()
     Return the current working directory.


File: octave,  Node: Password Database Functions,  Next: Group Database Functions,  Prev: Current Working Directory,  Up: System Utilities

Password Database Functions
===========================

   Octave's password database functions return information in a
structure with the following fields.

`name'
     The user name.

`passwd'
     The encrypted password, if available.

`uid'
     The numeric user id.

`gid'
     The numeric group id.

`gecos'
     The GECOS field.

`dir'
     The home directory.

`shell'
     The initial shell.

   In the descriptions of the following functions, this data structure
is referred to as a PW_STRUCT.

 - Loadable Function: PW_STRUCT =  getpwent ()
     Return a structure containing an entry from the password database,
     opening it if necessary. Once the end of the data has been reached,
     `getpwent' returns 0.

 - Loadable Function: PW_STRUCT =  getpwuid (UID).
     Return a structure containing the first entry from the password
     database with the user ID UID.  If the user ID does not exist in
     the database, `getpwuid' returns 0.

 - Loadable Function: PW_STRUCT =  getpwnam (NAME)
     Return a structure containing the first entry from the password
     database with the user name NAME.  If the user name does not exist
     in the database, `getpwname' returns 0.

 - Loadable Function:  setpwent ()
     Return the internal pointer to the beginning of the password
     database.

 - Loadable Function:  endpwent ()
     Close the password database.


File: octave,  Node: Group Database Functions,  Next: System Information,  Prev: Password Database Functions,  Up: System Utilities

Group Database Functions
========================

   Octave's group database functions return information in a structure
with the following fields.

`name'
     The user name.

`passwd'
     The encrypted password, if available.

`gid'
     The numeric group id.

`mem'
     The members of the group.

   In the descriptions of the following functions, this data structure
is referred to as a GRP_STRUCT.

 - Loadable Function: GRP_STRUCT = getgrent ()
     Return an entry from the group database, opening it if necessary.
     Once the end of the data has been reached, `getgrent' returns 0.

 - Loadable Function: GRP_STRUCT = getgrgid (GID).
     Return the first entry from the group database with the group ID
     GID.  If the group ID does not exist in the database, `getgrgid'
     returns 0.

 - Loadable Function: GRP_STRUCT = getgrnam (NAME)
     Return the first entry from the group database with the group name
     NAME.  If the group name does not exist in the database,
     `getgrname' returns 0.

 - Loadable Function:  setgrent ()
     Return the internal pointer to the beginning of the group database.

 - Loadable Function:  endgrent ()
     Close the group database.


File: octave,  Node: System Information,  Prev: Group Database Functions,  Up: System Utilities

System Information
==================

 - Built-in Function:  computer ()
     Print or return a string of the form CPU-VENDOR-OS that identifies
     the kind of computer Octave is running on.  If invoked with an
     output argument, the value is returned instead of printed.  For
     example,

          computer ()
               -| i586-pc-linux-gnu
          
          x = computer ()
               => x = "i586-pc-linux-gnu"

 - Built-in Function:  isieee ()
     Return 1 if your computer claims to conform to the IEEE standard
     for floating point calculations.

 - Built-in Variable: OCTAVE_VERSION
     The version number of Octave, as a string.

 - Built-in Function:  octave_config_info (OPTION)
     Return a structure containing configuration and installation
     information for Octave.

     if OPTION is a string, return the configuration information for the
     specified option.


 - Loadable Function:  getrusage ()
     Return a structure containing a number of statistics about the
     current Octave process.  Not all fields are available on all
     systems.  If it is not possible to get CPU time statistics, the
     CPU time slots are set to zero.  Other missing data are replaced
     by NaN.  Here is a list of all the possible fields that can be
     present in the structure returned by `getrusage':

    `idrss'
          Unshared data size.

    `inblock'
          Number of block input operations.

    `isrss'
          Unshared stack size.

    `ixrss'
          Shared memory size.

    `majflt'
          Number of major page faults.

    `maxrss'
          Maximum data size.

    `minflt'
          Number of minor page faults.

    `msgrcv'
          Number of messages received.

    `msgsnd'
          Number of messages sent.

    `nivcsw'
          Number of involuntary context switches.

    `nsignals'
          Number of signals received.

    `nswap'
          Number of swaps.

    `nvcsw'
          Number of voluntary context switches.

    `oublock'
          Number of block output operations.

    `stime'
          A structure containing the system CPU time used.  The
          structure has the elements `sec' (seconds) `usec'
          (microseconds).

    `utime'
          A structure containing the user CPU time used.  The structure
          has the elements `sec' (seconds) `usec' (microseconds).

   % DO NOT EDIT!  Generated automatically by munge-texi.


File: octave,  Node: Tips,  Next: Trouble,  Prev: System Utilities,  Up: Top

Tips and Standards
******************

   This chapter describes no additional features of Octave.  Instead it
gives advice on making effective use of the features described in the
previous chapters.

* Menu:

* Style Tips::                  Writing clean and robust programs.
* Coding Tips::                 Making code run faster.
* Documentation Tips::          Writing readable documentation strings.
* Comment Tips::                Conventions for writing comments.
* Function Headers::            Standard headers for functions.


File: octave,  Node: Style Tips,  Next: Coding Tips,  Prev: Tips,  Up: Tips

Writing Clean Octave Programs
=============================

   Here are some tips for avoiding common errors in writing Octave code
intended for widespread use:

   * Since all global variables share the same name space, and all
     functions share another name space, you should choose a short word
     to distinguish your program from other Octave programs.  Then take
     care to begin the names of all global variables, constants, and
     functions with the chosen prefix.  This helps avoid name conflicts.

     If you write a function that you think ought to be added to Octave
     under a certain name, such as `fiddle_matrix', don't call it by
     that name in your program.  Call it `mylib_fiddle_matrix' in your
     program, and send mail to (bug-octave@bevo.che.wisc.edu)
     suggesting that it be added to Octave.  If and when it is, the
     name can be changed easily enough.

     If one prefix is insufficient, your package may use two or three
     alternative common prefixes, so long as they make sense.

     Separate the prefix from the rest of the symbol name with an
     underscore `_'.  This will be consistent with Octave itself and
     with most Octave programs.

   * When you encounter an error condition, call the function `error'
     (or `usage').  The `error' and `usage' functions do not return.
     *Note Errors::.

   * Please put a copyright notice on the file if you give copies to
     anyone.  Use the same lines that appear at the top of the function
     files distributed with Octave.  If you have not signed papers to
     assign the copyright to anyone else, then place your name in the
     copyright notice.

