Memmap in MATLAB for huge arrays

Question

I want to create a memmap in MATLAB. In python I could do this by:

ut = np.memmap('my_array.mmap', dtype=np.float64, mode='w+', shape=(140000,3504))

Then I use it as a normal array, the OS ensured my memory never overflowed. How to do this in MATLAB?

From the docs it seems it wants me to create some array in MATLAB first then write it to a file and read using memmap!

Matlab docs are not clear enough: Please provide an example of creating an random array of size (140000,15000) and multiply it some other similar matrix.

Answer 1

You have to create an empty file first, then use memmapfile:

size=[140000,3504];
filesize=0;
datatype='float64';
filename='my_array.dat';
fid=fopen(filename,'w+');
max_chunk_size=1000000;
%fills an empty file
while filesize<prod(size)
    to_write=min(prod(size)-filesize,max_chunk_size);
    filesize=filesize+fwrite(f, zeros(to_write,1), datatype);
end   
fclose(fid);
m = memmapfile(filename,'Format','double', 'Writable',true);