For statement - print on exactly 1 second

Hi!

I want to print some text (ex. test) 20 times, every 1 second. I tried with for statement:

close all;
clear all;

tic
for i=1:20
  toc
  disp('test');
  pause(i-toc);
end

If I run this code, I see that time drifts also for 20 ms from whole second (I know that It depends on many things, occupancy of CPU is for ex. one thing). Is any other option to come closer to the whole second?

Thank you! Best regards, Dejan

Answer 1

[Jan]

java.lang.Thread.sleep(t*1000) than is more accurate than pause(t)

tic;
for i=1:20
  toc
  disp('test');
  java.lang.Thread.sleep((i-toc)*1000);
end

["test" removed for compactness]
Elapsed time is 0.008428 seconds.
Elapsed time is 1.000497 seconds.
Elapsed time is 1.999536 seconds.
Elapsed time is 2.999586 seconds.
Elapsed time is 4.000012 seconds.
Elapsed time is 4.999816 seconds.
Elapsed time is 5.999633 seconds.
Elapsed time is 6.999679 seconds.
Elapsed time is 7.999731 seconds.
Elapsed time is 8.999758 seconds.
Elapsed time is 9.999807 seconds.
Elapsed time is 10.999854 seconds.
Elapsed time is 11.999904 seconds.
Elapsed time is 12.999952 seconds.
Elapsed time is 13.998999 seconds.
Elapsed time is 14.999047 seconds.
Elapsed time is 15.999100 seconds.
Elapsed time is 16.999148 seconds.
Elapsed time is 17.999193 seconds.
Elapsed time is 18.999260 seconds.

See http://undocumentedmatlab.com/blog/pause-for-the-better . But my measurements with pause look fairly accurate also.

Use a timer for triggering code after certain times.

[Dejan Hrovatin]

Jan Simon, thank you! This is exactly what I was looking for.

Answer 2

[Image Analyst]

Instead of pause(i-toc), use pause(1). Your way did not pause exactly 1 second every time - the time changed upon each iteration.

[Image Analyst]

If the time to complete each iteration changes, then you can use while and toc:

for i = 1 : 20
    startTime = tic;
    % Lengthy and variable code...
    % Wait until 1 second has passed
    elapsedTime = toc(startTime); % In seconds
    while  elapsedTime < 1
        elapsedTime = toc(startTime); % In seconds
    end
end

Answer 3

[Dejan Hrovatin]

I wrote pause(i-toc) because eventually I will have to do some another operations in the same loop. Each operation need some time, and if then I use pause(1), I think that I will make bigger "error", because the time taken by each operation is not always the same. Recently I found timer function in MATLAB (doc timer). I will try this.