### 32.3 Functions and Variables for Runtime Environment

System variable: maxima_tempdir

  `maxima_tempdir` names the directory in which Maxima creates some temporary files. In particular, temporary files for plotting are created in `maxima_tempdir`.

  The initial value of `maxima_tempdir` is the user’s home directory, if Maxima can locate it; otherwise Maxima makes a guess about a suitable directory.

  `maxima_tempdir` may be assigned a string which names a directory.

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  Categories: Global variables

System variable: maxima_userdir

  `maxima_userdir` names a directory which Maxima searches to find Maxima and Lisp files. (Maxima searches some other directories as well; `file_search_maxima` and `file_search_lisp` are the complete lists.)

  The initial value of `maxima_userdir` is a subdirectory of the user’s home directory, if Maxima can locate it; otherwise Maxima makes a guess about a suitable directory.

  `maxima_userdir` may be assigned a string which names a directory. However, assigning to `maxima_userdir` does not automatically change `file_search_maxima` and `file_search_lisp`; those variables must be changed separately.

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  Categories: Global variables

Function: room
`room` ()
`room` (true)
`room` (false)

  Prints out a description of the state of storage and stack management in Maxima. `room` calls the Lisp function of the same name.

  - `room ()` prints out a moderate description.
  - `room (true)` prints out a verbose description.
  - `room (false)` prints out a terse description.
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  Categories: Debugging

Function: sstatus (keyword, item)

  When keyword is the symbol `feature`, item is put on the list of system features. After `sstatus (keyword, item)` is executed, `status (feature, item)` returns `true`. If keyword is the symbol `nofeature`, item is deleted from the list of system features. This can be useful for package writers, to keep track of what features they have loaded in.

  See also `status`.

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  Categories: Programming

Function: status
`status` (`feature`)
`status` (`feature`, item)

  Returns information about the presence or absence of certain system-dependent features.

  - `status (feature)` returns a list of system features. These include Lisp version, operating system type, etc. The list may vary from one Lisp type to another.
  - `status (feature, item)` returns `true` if item is on the list of items returned by `status (feature)` and `false` otherwise. `status` quotes the argument item. The quote-quote operator `''` defeats quotation. A feature whose name contains a special character, such as a hyphen, must be given as a string argument. For example, `status (feature, "ansi-cl")`.

  See also `sstatus`.

  The variable `features` contains a list of features which apply to mathematical expressions. See `features` and `featurep` for more information.

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  Categories: Programming

Function: system (command)

  Executes command as a separate process. The command is passed to the default shell for execution. `system` is not supported by all operating systems, but generally exists in Unix and Unix-like environments.

  Supposing `_hist.out` is a list of frequencies which you wish to plot as a bar graph using `xgraph`.

      (%i1) (with_stdout("_hist.out",
                 for i:1 thru length(hist) do (
                   print(i,hist[i]))),
             system("xgraph -bar -brw .7 -nl < _hist.out"));

  In order to make the plot be done in the background (returning control to Maxima) and remove the temporary file after it is done do:

      system("(xgraph -bar -brw .7 -nl < _hist.out;  rm -f _hist.out)&")

Function: time (%o1, %o2, %o3, …)

  Returns a list of the times, in seconds, taken to compute the output lines `%o1`, `%o2`, `%o3`, … The time returned is Maxima’s estimate of the internal computation time, not the elapsed time. `time` can only be applied to output line variables; for any other variables, `time` returns `unknown`.

  Set `showtime: true` to make Maxima print out the computation time and elapsed time with each output line.

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  Categories: Debugging

Function: timedate
`timedate` (T, tz_offset)
`timedate` (T)
`timedate` ()

  `timedate(T, tz_offset)` returns a string representing the time T in the time zone tz_offset. The string format is `YYYY-MM-DD HH:MM:SS.NNN[+|-]ZZ:ZZ` (using as many digits as necessary to represent the fractional part) if T has a nonzero fractional part, or `YYYY-MM-DD HH:MM:SS[+|-]ZZ:ZZ` if its fractional part is zero.

  T measures time, in seconds, since midnight, January 1, 1900, in the GMT time zone.

  tz_offset measures the offset of the time zone, in hours, east (positive) or west (negative) of GMT. tz_offset must be an integer, rational, or float between -24 and 24, inclusive. If tz_offset is not a multiple of 1/60, it is rounded to the nearest multiple of 1/60.

  `timedate(T)` is equivalent to `timedate(T, tz_offset)` with tz_offset equal to the offset of the local time zone.

  `timedate()` is equivalent to `timedate(absolute_real_time())`. That is, it returns the current time in the local time zone.

  Example:

  `timedate` with no argument returns a string representing the current time and date.

      (%i1) d : timedate ();
      (%o1)                      2010-06-08 04:08:09+01:00
      (%i2) print ("timedate reports current time", d) $
      timedate reports current time 2010-06-08 04:08:09+01:00

  `timedate` with an argument returns a string representing the argument.

      (%i1) timedate (0);
      (%o1)                      1900-01-01 01:00:00+01:00
      (%i2) timedate (absolute_real_time () - 7*24*3600);
      (%o2)                      2010-06-01 04:19:51+01:00

  `timedate` with optional timezone offset.

      (%i1) timedate (1000000000, -9.5);
      (%o1)               1931-09-09 16:16:40-09:30

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  Categories: Time and date functions

Function: parse_timedate
`parse_timedate` (S)

  Parses a string S representing a date or date and time of day and returns the number of seconds since midnight, January 1, 1900 GMT. If there is a nonzero fractional part, the value returned is a rational number, otherwise, it is an integer. `parse_timedate` returns `false` if it cannot parse S according to any of the allowed formats.

  The string S must have one of the following formats, optionally followed by a timezone designation:

  - `YYYY-MM-DD[ T]hh:mm:ss[,.]nnn`
  - `YYYY-MM-DD[ T]hh:mm:ss`
  - `YYYY-MM-DD`

  where the fields are year, month, day, hours, minutes, seconds, and fraction of a second, and square brackets indicate acceptable alternatives. The fraction may contain one or more digits.

  Except for the fraction of a second, each field must have exactly the number of digits indicated: four digits for the year, and two for the month, day of the month, hours, minutes, and seconds.

  A timezone designation must have one of the following forms:

  - `[+-]hh:mm`
  - `[+-]hhmm`
  - `[+-]hh`
  - `Z`

  where `hh` and `mm` indicate hours and minutes east (`+`) or west (`-`) of GMT. The timezone may be from +24 hours (inclusive) to -24 hours (inclusive).

  A literal character `Z` is equivalent to `+00:00` and its variants, indicating GMT.

  If no timezone is indicated, the time is assumed to be in the local time zone.

  Any leading or trailing whitespace (space, tab, newline, and carriage return) is ignored, but any other leading or trailing characters cause `parse_timedate` to fail and return `false`.

  See also `timedate` and `absolute_real_time`.

  Examples:

  Midnight, January 1, 1900, in the local time zone, in each acceptable format. The result is the number of seconds the local time zone is ahead (negative result) or behind (positive result) GMT. In this example, the local time zone is 8 hours behind GMT.

      (%i1) parse_timedate ("1900-01-01 00:00:00,000");
      (%o1)                         28800
      (%i2) parse_timedate ("1900-01-01 00:00:00.000");
      (%o2)                         28800
      (%i3) parse_timedate ("1900-01-01T00:00:00,000");
      (%o3)                         28800
      (%i4) parse_timedate ("1900-01-01T00:00:00.000");
      (%o4)                         28800
      (%i5) parse_timedate ("1900-01-01 00:00:00");
      (%o5)                         28800
      (%i6) parse_timedate ("1900-01-01T00:00:00");
      (%o6)                         28800
      (%i7) parse_timedate ("1900-01-01");
      (%o7)                         28800

  Midnight, January 1, 1900, GMT, in different indicated time zones.

      (%i1) parse_timedate ("1900-01-01 19:00:00+19:00");
      (%o1)                           0
      (%i2) parse_timedate ("1900-01-01 07:00:00+07:00");
      (%o2)                           0
      (%i3) parse_timedate ("1900-01-01 01:00:00+01:00");
      (%o3)                           0
      (%i4) parse_timedate ("1900-01-01Z");
      (%o4)                           0
      (%i5) parse_timedate ("1899-12-31 21:00:00-03:00");
      (%o5)                           0
      (%i6) parse_timedate ("1899-12-31 13:00:00-11:00");
      (%o6)                           0
      (%i7) parse_timedate ("1899-12-31 08:00:00-16:00");
      (%o7)                           0

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  Categories: Time and date functions

Function: encode_time
`encode_time` (year, month, day, hours, minutes, seconds, tz_offset)
`encode_time` (year, month, day, hours, minutes, seconds)

  Given a time and date specified by year, month, day, hours, minutes, and seconds, `encode_time` returns the number of seconds (possibly including a fractional part) since midnight, January 1, 1900 GMT.

  year must be an integer greater than or equal to 1899. However, 1899 is allowed only if the resulting encoded time is greater than or equal to 0.

  month must be an integer from 1 to 12, inclusive.

  day must be an integer from 1 to n, inclusive, where n is the number of days in the month specified by month.

  hours must be an integer from 0 to 23, inclusive.

  minutes must be an integer from 0 to 59, inclusive.

  seconds must be an integer, rational, or float greater than or equal to 0 and less than 60. When seconds is not an integer, `encode_time` returns a rational, such that the fractional part of the return value is equal to the fractional part of seconds. Otherwise, seconds is an integer, and the return value is likewise an integer.

  tz_offset measures the offset of the time zone, in hours, east (positive) or west (negative) of GMT. tz_offset must be an integer, rational, or float between -24 and 24, inclusive. If tz_offset is not a multiple of 1/3600, it is rounded to the nearest multiple of 1/3600.

  If tz_offset is not present, the offset of the local time zone is assumed.

  See also `decode_time`.

  Examples:

      (%i1) encode_time (1900, 1, 1, 0, 0, 0, 0);
      (%o1)                           0
      (%i2) encode_time (1970, 1, 1, 0, 0, 0, 0);
      (%o2)                      2208988800
      (%i3) encode_time (1970, 1, 1, 8, 30, 0, 8.5);
      (%o3)                      2208988800
      (%i4) encode_time (1969, 12, 31, 16, 0, 0, -8);
      (%o4)                      2208988800
      (%i5) encode_time (1969, 12, 31, 16, 0, 1/1000, -8);
                                2208988800001
      (%o5)                     -------------
                                    1000
      (%i6) % - 2208988800;
                                     1
      (%o6)                         ----
                                    1000

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  Categories: Time and date functions

Function: decode_time
`decode_time` (T, tz_offset)
`decode_time` (T)

  Given the number of seconds (possibly including a fractional part) since midnight, January 1, 1900 GMT, returns the date and time as represented by a list comprising the year, month, day of the month, hours, minutes, seconds, and time zone offset.

  tz_offset measures the offset of the time zone, in hours, east (positive) or west (negative) of GMT. tz_offset must be an integer, rational, or float between -24 and 24, inclusive. If tz_offset is not a multiple of 1/3600, it is rounded to the nearest multiple of 1/3600.

  If tz_offset is not present, the offset of the local time zone is assumed.

  See also `encode_time`.

  Examples:

      (%i1) decode_time (0, 0);
      (%o1)               [1900, 1, 1, 0, 0, 0, 0]
      (%i2) decode_time (0);
      (%o2)             [1899, 12, 31, 16, 0, 0, - 8]
      (%i3) decode_time (2208988800, 9.25);
                                                37
      (%o3)              [1970, 1, 1, 9, 15, 0, --]
                                                4
      (%i4) decode_time (2208988800);
      (%o4)             [1969, 12, 31, 16, 0, 0, - 8]
      (%i5) decode_time (2208988800 + 1729/1000, -6);
                                            1729
      (%o5)           [1969, 12, 31, 18, 0, ----, - 6]
                                            1000
      (%i6) decode_time (2208988800 + 1729/1000);
                                            1729
      (%o6)           [1969, 12, 31, 16, 0, ----, - 8]
                                            1000

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  Categories: Time and date functions

Function: absolute_real_time ()

  Returns the number of seconds since midnight, January 1, 1900 GMT. The return value is an integer.

  See also `elapsed_real_time` and `elapsed_run_time`.

  Example:

      (%i1) absolute_real_time ();
      (%o1)                      3385045277
      (%i2) 1900 + absolute_real_time () / (365.25 * 24 * 3600);
      (%o2)                   2007.265612087104

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  Categories: Time and date functions

Function: elapsed_real_time ()

  Returns the number of seconds (including fractions of a second) since Maxima was most recently started or restarted. The return value is a floating-point number.

  See also `absolute_real_time` and `elapsed_run_time`.

  Example:

      (%i1) elapsed_real_time ();
      (%o1)                       2.559324
      (%i2) expand ((a + b)^500)$
      (%i3) elapsed_real_time ();
      (%o3)                       7.552087

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  Categories: Time and date functions

Function: elapsed_run_time ()

  Returns an estimate of the number of seconds (including fractions of a second) which Maxima has spent in computations since Maxima was most recently started or restarted. The return value is a floating-point number.

  See also `absolute_real_time` and `elapsed_real_time`.

  Example:

      (%i1) elapsed_run_time ();
      (%o1)                         0.04
      (%i2) expand ((a + b)^500)$
      (%i3) elapsed_run_time ();
      (%o3)                         1.26

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  Categories: Time and date functions