Matlab freeze when fprintf to file

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Michael Madelaire
编辑： Stephen23 2018-8-4
Hi
I have a large amount of data, many years. It is given in daily files.
For reasons irrelevant for the question I have to combine these files to yearly data files ~ 3Gb.
The daily files are of .cdf format and contain more variables than needed and also lack some that has to be derived.
The following shows an example that makes my computer freeze for around 5 min. But that data datafile is complete with seconds.
fid = fopen('test.m', 'w');
data = randi(5, 40000, 10);
for i=1:2 %5
fprintf(fid, '%d %d %d %d %d %d %d %d %d %d\n', data);
end
fprintf(fid, '%d %d %d %d %d %d %d %d %d %d\n', zeros(1, 10)); %Newly added line
fclose(fid)
Does anyone know why it freezes for so long when the files is written so fast?
Using Matlab R2018a on a remote desktop with Ubuntu OS
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Stephen23
Stephen23 2018-8-3
编辑：Stephen23 2018-8-3
@Michael Madelaire: this sounds similar to when many files are opened but not closed. When there are too many open file then MATLAB can become slow or unresponsive. Run fclose('all') and check your code carefully that it really closes all files properly.
How many files do you have open at once?
Michael Madelaire
Michael Madelaire 2018-8-3
@Stephen Cobeldick: Thanks for the comment. Although the code above is an example it is pretty much what is going on.
One file is opened.
Within the following loop data is loaded using cdfread:
data = cdfread(fullfile(base, filename{1}), ...
'Variables', { 'Timestamp', ...
'Latitude', 'Longitude', 'Radius', ...
'F', 'B_VFM', 'q_NEC_CRF', ...
'Flags_F', 'Flags_B', 'Flags_q', ...
'dB_Sun' }, ...
'ConvertEpochToDatenum', true, ...
'CombineRecords', true);
This data is written to the .m file using fprintf.
When the loop is complete the file is closed with fclose and a file is opened for the next year.

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OCDER
OCDER 2018-8-3
Instead of 'test.m', write to 'test.txt' or something else. The fprintf is fast, but having a "test.m" file in the current directory seems to freeze Matlab.
fid = fopen('test.txt', 'w'); %Don't write to .m files, unless it's a matlab file type
data = randi(5, 40000, 10);
for i=1:2 %5
fprintf(fid, '%d %d %d %d %d %d %d %d %d %d\n', data);
end
fprintf(fid, '%d %d %d %d %d %d %d %d %d %d\n', zeros(1, 10)); %Newly added line
fclose(fid)
My Matlab also freezes when there is a "test.m" file in the current directory that Matlab cannot determine if it's a script or function - it just says it's a "Matlab Code File". I'm guessing this step for determining what file type this "test.m" file is causes Matlab to freeze. I think this should go into the bug report for 2017 versions - not sure if 2018 version fixed this.
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Stephen23
Stephen23 2018-8-4
编辑：Stephen23 2018-8-4
"But I am getting a bit tired of this issue and am just going to use textscan."
Or you could just follow the instructions given in the error message.
Or use dlmread.
Both would be much simpler than using textscan.
Or use save and load (these are designed to be used together).
OCDER
OCDER 2018-8-4
do you want to save/load matlab variables?
data = randi(5, 40000, 10)
save('test.mat', 'data', '-v7.3', '-nocompression') %works for > 2GB files
S = load('test.mat', 'data')
S.data = %your 'data'.
https://www.mathworks.com/help/matlab/ref/save.html

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