Help for 'PAUSE' says
PAUSE(n) pauses for n seconds before continuing, where n can also be a
fraction. The resolution of the clock is platform specific. Fractional
pauses of 0.01 seconds should be supported on most platforms.
But in my case pause(0.01) doesn't do anything at all (pause, pause(n) with whole number n works)
Is there any way to make a millisecond level delay (50 ms, 100 ~ 500 ms) delay in matlab?
Matlab version is
MATLAB Version 7.9.0.529 (R2009b)
64 bit on a Windows 10 64 bit Home edition
I see two options. Let's call them the looping option and the native option. The first is just using a while loop to check if your desired time to wait is already reached. You can do this with MATLAB's stopwatch timer tic and toc. This is the normal time (not the CPU-time). As you are writing a loop, which runs at maximum speed, you might encounter a high CPU-usage but this should be OK if it is only for a couple of milliseconds.
%% looping
% desired time to wait
dt_des = 0.001; % 1 ms
% initialize clock
t_st = tic;
% looping
while toc(t_st) < dt_des
end
% read clock
toc(t_st)
The native option is using pause (make sure that you have enabled it once with pause('on')). I assumed from your question that this does not always work -- however, it does on my system (R2019b, windows 10).
%% use pause()
tic
pause(0.001)
toc
The results of both are
Elapsed time is 0.001055 seconds.
Elapsed time is 0.001197 seconds.
It's not too accurate but you might get better results if you tune the numbers on your PC.
you can also use
java.lang.Thread.sleep(10);
if you are using an old matlab version, see discussion here.
Related
I am running fmincon for a gird. For some points in the grid there is no solution, exit flag=-2, and it takes half an hour sometimes to return the flag and start the next point in the grid. However, for the other points the answer is revealed in less than a min.
So I thought one possible solution to reduce the unnecessary running time is to define a stop criteria based on elapsed time for each point in the grid. In other words, How to stop fmincon after running an elapsed time of T sec?
You can use an output function:
tic
fmincon(.....,optimset('OutputFcn',#outfun,'MaxFunEval',20000))
outfun.m :
function stop = outfun(x,optimValues,state)
stop = toc>T;
I am trying to use matlab for data acquisition with a licor820 instrument. The instrument outputs data at 2 hertz.
I have tried many different methods using infinite loops with asynchronous sampling (readasync) and timed readings but I am unable to get 2 hertz data. I am getting reads in the .51 s range. here are three examples of my methods. Any advice on what I may be doing wrong or how to properly sample at the highest frequency would be greatly appreciated!
example1: using readasync
tinit=tic; %initialization timer
s=serial('COM4') %,'InputBufferSize',40);
fopen(s)
while toc(tinit)<2 %allow time to initialize
end
while 1<2 %infinite loop for continuous sampling
readasync(s)
data=fscanf(s)
toc %allows me to see time between data acquisitions
tic
end
example 2: using bytes available.
My thinking here is to acquire data when I have the minimum amount of bytes necessary. Although I am unsure exactly how to determine how many bytes are necessary for my instrument, besides through visually looking at the data and narrowing it down to around 40 bytes:
while 1<2 %infinite loop for continuous sampling
if s.BytesAvailable >35
scandata=fscanf(s);
toc
tic
end
end
example 3: time forcing.
Since I need 2 hertz data my thinking here was to just force read the buffer every .49 seconds. The weird thing I see here is that it initially provides samples every .49 seconds, but while I monitor the bytes available at the port I see it steady dropping from 512 until it gets to 0 and then I stop getting .49 second samples. I guess I don't really understand how to use serial efficiently.
while 1<2 %infinite loop
if toc(t2)>=.49 %only sample after .49 seconds have passed
t2=tic; %reinitiate the tic for this forced time loop
bytes=s.BytesAvailable %to monitor how many bytes there are at the port
scandata=fscanf(s);
if ~isempty(scandata) && length(scandata)== 3 %checks for successful read
toc
tic
end
end
end
I feel there must be some way to sample completely in sync with the an instrument but I can't figure it out. Any help, suggestions, or ideas would be greatly appreciated! Thanks!
Dont rely on tic and toc. These functions use the time supplied by the OS calls. Mathworks claims to use high resolution timers, but do not rely on this! If you do not use a realtime OS these measurements are subject to unknown variation.
Sampling should be performed by realtime capable hardware. In your case I suspect that your sampling rate is actually controlled by your instrument. The output of the instrument is buffered by your serial interface. Therefore it seems to me that Matlab does not influence the sampling rate at all. (As long as the buffer does not overflow)
Try to acquire about 2000 samples or more and see how long it takes. Then divide the total time by the number of samples (-1) and compare this to the expected 0.5 s. If there is a difference, try adjusting the configuration of your instrument.
The matlab recording function"record ( recordObj, samplingTime )" needs 0.8 second plus the sampling time to be executed.
this means that if i want to record for only 0.2 second the execution time of this function will be 1 second.
I am working on a real time processing project in which I need to record 0.2 second files with high frequency and make real time processing on each file.
So i tried to record a long record and access it every 0.2 second.
So I wonder if i can access recordObj while the recording function is in progress .
I tried this code but i got error as the matlab couldn't access "myvoise" while recording is in progress. thanks in advance
clc
% clear all
% myVoice = audiorecorder;
% % Define callbacks to show when
% % recording starts and completes.
% myVoice.StartFcn = 'disp(''Start speaking.'')';
% myVoice.StopFcn = 'disp(''End of recording.'')';
% record(myVoice,20);
% y=getaudiodata(myVoice);
Unfortunately, Matlab is not really designed for real time processing. But if you really need it, look into the DSP Systems Toolbox, which provide this functionality.
You couldn't access myVoice because record is a not blocking function, this means that after execution of record(myVoice,20) immediately getaudiodata is executed but myVoice has not yet captured any data. If instead you use recordblocking(myVoice,20) then this will block flow of your code for 20 seconds. So myVoice now will contain data for 20 seconds and getaudiodata will be successfully executed.
Because you want real time operation I suggest set myVoice.TimerFcn = 'callbackfcn(myVoice)' and also set myVoice.TimerPeriod=period. Where callback fcn will be a user specified function in which you call data = getaudiodata(myVoice). This function will be called every period seconds during execution. So in this way you can call record(myVoice,20) and after period(s) getaudiodata will be successfully executed because myVoice already has period(in s) of audio data.
Be aware of that every time getaudiodata is executed will acquire all data of my voice from the beggining of recording, so you can skip every period the previous acquired data (i*period/Fs) where i is the time the callback function is executed(beginning from zero). Be also awhere of that myVoice will be buffered in memory, so if you record for a long period of time at high sampling frequency matlab performance will deteriorate
How can I measure the time used by Matlab in the execution of some commands? I am looking for something like linux time command, which returns the actual CPU used (user + sys), instead of the total time transcurred, which can vary depending on system usage by other processes.
Also, the time should be returned in milliseconds.
You can use cputime:
CPUTIME CPU time in seconds.
CPUTIME returns the CPU time in seconds that has been used
by the MATLAB process since MATLAB started.
For example:
t=cputime; your_operation; cputime-t
returns the cpu time used to run your_operation.
The return value may overflow the internal representation
and wrap around.
There's also timeit.
And you can also use tic/ toc (see Daniel's answer).
See some useful comments on measuring CPU time. According to the above link, tic / toc and timeit give more accurate estimations than cputime.
For a simple clock time solution, use tic and toc
profile provides a detailed report code per line, you can choose between cpu time and real time.
I am reading a 40 MB file with three different ways. But the first one is way faster than the 2 others. Do you guys have an idea why ? I would rather implement condition in loops or whiles to separate data than load everything with the first quick method and separate them then - memory saving -
LL=10000000;
fseek(fid,startbytes, 'bof');
%% Read all at once %%%%%%%%%%%%%%%%%%%%%%
tic
AA(:,1)=int32(fread(fid,LL,'int32'));
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fseek(fid,startbytes,'bof');
%% Read all using WHILE loop %%%%%%%%%%%%%
tic
i=0;
AA2=int32(zeros(LL,1));
while i<LL
i=i+1;
AA2(i,1)=fread(fid,1,'int32');
end
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fseek(fid,startbytes,'bof');
%% Read all using FOR loop %%%%%%%%%%%%%%%
tic
AA3=int32(zeros(LL,1));
for i=1:LL
AA3(i,1)=fread(fid,1,'int32');
end
toc
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Elapsed time is 0.312916 seconds.
Elapsed time is 138.811520 seconds.
Elapsed time is 116.799286 seconds.
Here are my two cents on this:
Is the JIT accelerator enabled?
Since MATLAB is an interpreted language, for loops can be quite slow. while loops may be even slower, because the termination condition is re-evaluted in each iteration (unlike for loops that iterate a predetermined number of times). Nevertheless, this is not so true with JIT acceleration, which can significantly boost their performance.
I'm not near MATLAB at the moment, so I cannot reproduce this scenario myself, but you can check yourself whether you have JIT acceleration turned on by typing the following in the command window:
feature accel
If the result is 0 it means that it's disabled, and this is probably the reason for the huge reduction in performance.
Too many system calls?
I'm not familiar with the internals of fread, but I can only assume that one fread call to read the entire file invokes less system calls than multiple fread calls. System calls are usually expensive, so this can, to some extent, account for the slowdown.