clock

Current date and time.

Syntax

t = clock

Description

clock returns a 1x6 row vector, containing the year (four digits), the month, the day, the hour, the minute and the second of the current local date and time. All numbers are integers, except for the seconds which are fractional. The absolute precision is plus or minus one second with respect to the computer's clock; the relative precision is plus or minus 1 microsecond on a Macintosh, and plus or minus 1 millisecond on Windows.

Example

clock
  1999 3 11 15 37 34.9167

See also

posixtime, tic, toc

posixtime

Current Posix time.

Syntax

t = posixtime

Description

posixtime returns the Posix time, the integral number of seconds since 1 February 1970 at 00:00:00 UTC, based on the value provided by the operating system.

Example

posixtime
  1438164887

See also

clock

tic

Start stopwatch.

Syntax

tic
t0 = tic
tic(CPUTime=true)
t0 = tic(CPUTime=true)

Description

Without output argument, tic resets the stopwatch. Typically, tic is used once at the beginning of the block to be timed, and toc at the end. toc can be called multiple times to get intermediate times.

With an output argument, tic gets the current state of the stopwatch. Multiple independent time measurements can be performed by passing this value to toc.

By default, tic and toc are based on the real, "wall-clock" time. tic(CPUTime=true) is based on CPU time instead, which gives more accurate results for non-multithreaded programs. Measurements made with wall-clock time and CPU time are independent and can be mixed freely.

See also

toc, clock

toc

Elapsed time of stopwatch.

Syntax

elapsed_time = toc
elapsed_time = toc(t0)
elapsed_time = toc(CPUTime=true)
elapsed_time = toc(t0, CPUTime=true)

Description

Without input argument, toc gets the time elapsed since the last execution of tic without output argument. Typically, toc is used at the end of the block of statements to be timed.

With an input argument, toc(t0) gets the time elapsed since the execution of t0=tic. Multiple independent time measurements, nested or overlapping, can be performed simultaneously.

With a named argument, toc(CPUTime=true) or toc(t0,CPUTime=true) use CPU time: toc measures only the time spent in the LME application. Other processes do not have a large impact. For instance, typing tic(CPUTime=true) at the command-line prompt, waiting 5 seconds, and typing toc(CPUTime=true) will show a value much smaller than 5; while typing tic and toc will show the same elapsed time a chronograph would. CPU time is usually more accurate for non-multithreaded code, and wall-clock time for multi-threaded code, or measurements involving devices or network communication.

Examples

Time spent to compute the eigenvalues of a random matrix:

tic; x = eig(rand(200)); toc
  0.3046

Percentage of time spent in computing eigenvalues in a larger program:

eigTime = 0;
s = [];
tic(CPUTime=true);
for i = 1:100
  A = randn(20);
  eigT0 = tic(CPUTime=true);
  s1 = eig(A);
  eigTime = eigTime + toc(eigT0, CPUTime=true);
  s = [s, s1];
end
totalTime = toc(CPUTime=true);
100 * eigTime / totalTime
  78.4820

See also

tic, clock