Clash Royale CLAN TAG#URR8PPP

In the following code, why does Matlab alternate between fast and slow reads?

I am experiencing some strange behaviour in an code that reads a matrix from the hard disk.

I first write a binary file to the hard disk containing a matrix a:

a

N=17000;
a=rand(N);
fid=fopen('a','Wb');
fwrite(fid, a, 'double');
fclose(fid);


Now, I try reading the opening, reading, and closing the file to see how long the whole procedure takes. Each iteration should take the same amount of time.

for ii=1:10
tic
fid = fopen('a', 'r');
matrix=fread(fid, [N, N], 'double');
fclose(fid);
toc
end


Interestingly, the time it takes to read the file alternates between fast and slow! Is there any explanation for this? Here are the timings for the above loop:

Elapsed time is 1.259988 seconds.
Elapsed time is 2.454427 seconds.
Elapsed time is 1.534250 seconds.
Elapsed time is 2.453246 seconds.
Elapsed time is 1.535322 seconds.
Elapsed time is 2.454762 seconds.
Elapsed time is 1.534847 seconds.
Elapsed time is 2.449777 seconds.
Elapsed time is 1.534265 seconds.
Elapsed time is 2.449074 seconds.


1 Answer
1

That's very interesting, I wonder if it has to do with the preceding of opening it closing a file. A way to test that possibility may be to add delay(2) in the loop and then see if the times match.

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