How to iteratively save a 3d array to a .mat file without storing the array in the workspace to conserve memory?

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sbenit
sbenit 2023-3-21
回答： Abhijeet 2023-4-4
I've tried this two ways. The first way is to create a structure Psi, then iteratively save the fields p1, p2,... pn into the same structure in the .mat file; however, this forces me to create a new Psi variable while the original psi is still in memory. I'd like to avoid that step if I can.
I've changed some things about the original code to make it more readable.
blksize = 100;
for iblks = 1:blksize:nprofiles
blockids = iblks : min(iblks+blksize-1,nprofiles);
psi = nan(1000,3000,blksize);
zout = nan(1000,1,blksize);
rout = nan(1,3000,blksize);
parfor issp = 1:blksize
[psi(:,:,issp), zout(:,:,issp), rout(:,:,issp)]=ram(inputs);
end
Psi = struct(['p' num2str(iblks)], psi);
clearvars psi
save('F:\Thesis_data\winter_psi', '-struct', 'Psi', ['p' num2str(iblks)])
end
The second way I used matfile.m like this:
m = matfile('directory\winter_psi_', 'Writable', true);
m.psi = [];
for iblks = 1:blksize:nprofiles
blockids = iblks : min(iblks+blksize-1,nprofiles);
psi = nan(1000,3000,blksize);
zout = nan(1000,1,blksize);
rout = nan(1,3000,blksize);
if iblks == 1
parfor issp = 1:blksize
[psi(:,:,issp), zout(:,:,issp), rout(:,:,issp)]= ram(inputs)
end
m.psi = psi;
clearvars psi
else
parfor issp = 1:blksize
[psi(:,:,issp), ~, ~]= ram(inputs);
end
m.psi(:,:,iblks) = psi;
clearvars psi
end
end % iblks
Unfortunately, m.psi is saved in the workspace in the Matfile object m.
Is there a way to save psi iteratively to a .mat file without storing a new variable in the workspace?

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回答（1 个）

Abhijeet
Abhijeet 2023-4-4
Hi,
Yes, you can use the matfile function in MATLAB to iteratively save a 3D array to a .mat file without storing the array in the workspace to conserve memory.
Here's a sample code :
m = matfile(filename, 'Writable', true);
for i = 1:N
% calculate the ith slice of psi
psi_i = calculate_psi_i(i);
% write psi_i to the matfile
m.psi(:,:,i) = psi_i;
end
Inside the loop, the calculate_psi_i function is used to calculate the ith slice of the 3D array psi. This slice is then saved to the matfile using the syntax m.psi(:,:,i) = psi_i.
Note : This syntax does not create a new variable in the workspace, but instead writes directly to the matfile on disk. The matfile is automatically closed when the script finishes running.
Thanks

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