Timing Utilities - Untitled
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### 35.1 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.

> See also: strftime, strptime, localtime, gmtime, mktime, now, date, clock, datenum, datestr, datevec, calendar, weekday.

— Function File: t = now ()

> Returns the current local time as the number of days since Jan 1, 0000. By this reckoning, Jan 1, 1970 is day number 719529.

> The integral part, `floor (now)` corresponds to 00:00:00 today.

> The fractional part, `rem (now, 1)` corresponds to the current time on Jan 1, 0000.

> The returned value is also called a "serial date number" (see `datenum`).

> See also: clock, date, datenum.

— 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\n"

— 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
>                        }

> See also: strftime, strptime, localtime, mktime, time, now, date, clock, datenum, datestr, datevec, calendar, weekday.

— 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
>                        }

> See also: strftime, strptime, gmtime, mktime, time, now, date, clock, datenum, datestr, datevec, calendar, weekday.

— 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

> See also: strftime, strptime, localtime, gmtime, time, now, date, clock, datenum, datestr, datevec, calendar, weekday.

— 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 (fmt, tm_struct)

> Format the time structure tm_struct in a flexible way using the format string fmt that contains ``%`' 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-).

> See also: strptime, localtime, gmtime, mktime, time, now, date, clock, datenum, datestr, datevec, calendar, weekday.

— Loadable Function: [tm_struct, nchars] = strptime (str, fmt)

> Convert the string str to the time structure tm_struct under the control of the format string fmt.

> If fmt fails to match, nchars is 0; otherwise it is set to the position of last matched character plus 1. Always check for this unless you're absolutely sure the date string will be parsed correctly.

> See also: strftime, localtime, gmtime, mktime, time, now, date, clock, datenum, datestr, datevec, calendar, weekday.

Most of the remaining functions described in this section are not patterned after the standard C library. Some are available for compatibility 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.

> See also: tic, toc, clock, cputime.

— Built-in Function: [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

— Built-in Function: tic ()
— Built-in Function: toc ()

> Set or check a wall-clock timer. Calling `tic` without an output argument sets the timer. Subsequent calls to `toc` return the number of seconds since the timer was set. 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 called with one output argument then this function returns a scalar of type `uint64` and the wall-clock timer is not started.

>               t = tic; sleep (5); (double (tic ()) - double (t)) * 1e-6
>                    => 5

> Nested timing with `tic` and `toc` is not supported. Therefore `toc` will always return the elapsed time from the most recent call to `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...\n");
>               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.

— Function File: str = datestr (date, [f, [p]])

> Format the given date/time according to the format `f` and return the result in str. date is a serial date number (see `datenum`) or a date vector (see `datevec`). The value of date may also be a string or cell array of strings.

> f can be an integer which corresponds to one of the codes in the table below, or a date format string.

> p is the year at the start of the century in which two-digit years are to be interpreted in. If not specified, it defaults to the current year minus 50.

> For example, the date 730736.65149 (2000-09-07 15:38:09.0934) would be formatted as follows:

> Code | Format | Example
> --- | --- | ---
> 0 | dd-mmm-yyyy HH:MM:SS | 07-Sep-2000 15:38:09
> 1 | dd-mmm-yyyy | 07-Sep-2000
> 2 | mm/dd/yy | 09/07/00
> 3 | mmm | Sep
> 4 | m | S
> 5 | mm | 09
> 6 | mm/dd | 09/07
> 7 | dd | 07
> 8 | ddd | Thu
> 9 | d | T
> 10 | yyyy | 2000
> 11 | yy | 00
> 12 | mmmyy | Sep00
> 13 | HH:MM:SS | 15:38:09
> 14 | HH:MM:SS PM | 03:38:09 PM
> 15 | HH:MM | 15:38
> 16 | HH:MM PM | 03:38 PM
> 17 | QQ-YY | Q3-00
> 18 | QQ | Q3
> 19 | dd/mm | 13/03
> 20 | dd/mm/yy | 13/03/95
> 21 | mmm.dd.yyyy HH:MM:SS | Mar.03.1962 13:53:06
> 22 | mmm.dd.yyyy | Mar.03.1962
> 23 | mm/dd/yyyy | 03/13/1962
> 24 | dd/mm/yyyy | 12/03/1962
> 25 | yy/mm/dd | 95/03/13
> 26 | yyyy/mm/dd | 1995/03/13
> 27 | QQ-YYYY | Q4-2132
> 28 | mmmyyyy | Mar2047
> 29 | yyyymmdd | 20470313
> 30 | yyyymmddTHHMMSS | 20470313T132603
> 31 | yyyy-mm-dd HH:MM:SS | 1047-03-13 13:26:03

> If f is a format string, the following symbols are recognised:

> Symbol | Meaning | Example
> --- | --- | ---
> yyyy | Full year | 2005
> yy | Two-digit year | 2005
> mmmm | Full month name | December
> mmm | Abbreviated month name | Dec
> mm | Numeric month number (padded with zeros) | 01, 08, 12
> m | First letter of month name (capitalized) | D
> dddd | Full weekday name | Sunday
> ddd | Abbreviated weekday name | Sun
> dd | Numeric day of month (padded with zeros) | 11
> d | First letter of weekday name (capitalized) | S
> HH | Hour of day, padded with zeros if PM is set | 09:00
> | and not padded with zeros otherwise | 9:00 AM
> MM | Minute of hour (padded with zeros) | 10:05
> SS | Second of minute (padded with zeros) | 10:05:03
> PM | Use 12-hour time format | 11:30 PM

> If f is not specified or is `-1`, then use 0, 1 or 16, depending on whether the date portion or the time portion of date is empty.

> If p is nor specified, it defaults to the current year minus 50.

> If a matrix or cell array of dates is given, a vector of date strings is returned.

> See also: datenum, datevec, date, clock, now, datetick.

— Function File: v = datevec (date)
— Function File: v = datevec (date, f)
— Function File: v = datevec (date, p)
— Function File: v = datevec (date, f, p)
— Function File: [y, m, d, h, mi, s] = datevec (...)

> Convert a serial date number (see `datenum`) or date string (see `datestr`) into a date vector.

> A date vector is a row vector with six members, representing the year, month, day, hour, minute, and seconds respectively.

> f is the format string used to interpret date strings (see `datestr`).

> p is the year at the start of the century in which two-digit years are to be interpreted in. If not specified, it defaults to the current year minus 50.

> See also: datenum, datestr, date, clock, now.

— Function File: calendar (...)
— Function File: c = calendar ()
— Function File: c = calendar (d)
— Function File: c = calendar (y, m)

> If called with no arguments, return the current monthly calendar in a 6x7 matrix.

> If d is specified, return the calendar for the month containing the day d, which must be a serial date number or a date string.

> If y and m are specified, return the calendar for year y and month m.

> If no output arguments are specified, print the calendar on the screen instead of returning a matrix.

> See also: datenum.

— Function File: [n, s] = weekday (d, [form])

> Return the day of week as a number in n and a string in s, for example `[1, "Sun"]`, `[2, "Mon"]`, ..., or `[7, "Sat"]`.

> d is a serial date number or a date string.

> If the string form is given and is `"long"`, s will contain the full name of the weekday; otherwise (or if form is `"short"`), s will contain the abbreviated name of the weekday.

> See also: datenum, datevec, eomday.

— Function File: e = eomday (y, m)

> Return the last day of the month m for the year y.

> See also: datenum, datevec, weekday, eomdate.