TIMER
Compute Elapsed Time

TIMER is a directory of MATLAB programs which compute the elapsed CPU time or wallclock time of a part of a calculation.

The idea is that you want to determine the amount of CPU time taken by a piece of your code, so you write lines like this:

        t_start = timer;

        ...some big calculation...

        t_stop = timer;

        fprintf ( 1, 'Elapsed CPU time = %f\n', t_stop - t_start );
      

MATLAB includes a function CPUTIME, which returns the CPU time in seconds. This represents the amount of computer time "used" by your program, and could be somewhat less than the elapsed wall clock time.

MATLAB includes a function CLOCK which returns the YMDHMS date as a vector of six integers. Two values of CLOCK can be subtracted, and the difference, or elapsed "wall clock time", returned in seconds, by the function ETIME.

MATLAB includes two functions TIC and TOC. If TIC is called before something is to be timed, and TOC is called afterward, then TOC will either print the elapsed wallclock time if its value is not being copied to a variable, or return the value of the elapsed wallclock time to a variable.

For parallel programming, the important thing to measure is the elapsed wallclock time. This can be found by subtracting an initial reading of the wallclock time from a final one.

The OpenMP system provides a function used as follows:

        seconds = omp_get_wtime ( )
        operations to time;
        seconds = omp_get_wtime ( ) - seconds;
      

        seconds = MPI_Wtime ( );
        operations;
        seconds = MPI_Wtime ( ) - seconds;
      

        tic;
        operation;
        seconds = toc;
      

Licensing:

The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.

Related Data and Programs:

SUM_MILLION is a MATLAB program which sums the integers from 1 to 1,000,000, as a demonstration of how to rate a computer's speed;

TIMER is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

TIMESTAMP is a MATLAB library which prints out the current YMDHMS date.

TIMING_PARALLEL is a directory of MATLAB programs which illustrates how to time a parallel MATLAB program.

Examples and Tests:

CPUTIME_TEST uses the CPUTIME routine:

• timer_cputime_test.m, the main body of the test;
• timer_cputime_test01.m, test #1;
• timer_cputime_test02.m, test #2;
• timer_cputime_test03.m, test #3;
• timer_cputime_test04.m, test #4;
• timer_cputime_test_output.txt, output from the test;

ETIME_TEST uses the ETIME routine:

• timer_etime_test.m, the main body of the test;
• timer_etime_test01.m, test #1;
• timer_etime_test02.m, test #2;
• timer_etime_test03.m, test #3;
• timer_etime_test04.m, test #4;
• timer_etime_test_output.txt, output from the test;

TICTOC_TEST uses the TIC and TOC routine:

• timer_tictoc_test.m, the main body of the test;
• timer_tictoc_test01.m, test #1;
• timer_tictoc_test02.m, test #2;
• timer_tictoc_test03.m, test #3;
• timer_tictoc_test04.m, test #4;
• timer_tictoc_test_output.txt, output from the test;

There are a few auxilliary routines you may need:

• r8_huge.m, returns a "huge" value;
• timestamp.m, prints the YMDHMS date as a time stamp;

You can go up one level to the MATLAB source codes.