How to solve "Error while using repmat : out of memory"

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Zhixin Pan
Zhixin Pan 2019-1-4
评论： Zhixin Pan 2019-1-8
Hi all,
I was dealing with codes for image processing, where I need to use "repmat" function to create a big 5-d matrix, in a size of [116 116 72 64 64].
And it will give "out of memory" error.
The slice of code is shown below, it will give error when trying to assign new value to w (2nd row):
sq = repmat(sq, [1, 1, 1, 1, nd]);
w = repmat(reshape(w, [1, 1, 1, nd, nd]), [sx, sy, sz, 1, 1]);
raw = cat(4, s0, squeeze(sum(sq .* w, 4)));
Here , before these lines,
sq in [116 116 72 64]
w in [64, 64]
nd = 64, sx = sy = 116, sz = 72
What make things wield is, the size of matrix "sq" is in the same shape. And there will be no error when executing the first line of code, which means we could allocate enough space for a matrix in a size of [116 116 72 64 64].
As you can see, what I wanna do is creating w in the same shape as sp, and perform a element-wise multiplication. But the 2nd line will not work.
I tried to pre-allocate an empty matrix instead, by using zeros, but again get "out of memory" error.
Can anybody help me?
Thanks.

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Matt J
Matt J 2019-1-4
编辑：Matt J 2019-1-4
Forget about repmats. Use the original sq and w as follows,
tmp=reshape( reshape(sq,[],nd)*w , size(sq) );
raw = cat(4, s0, tmp);
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Matt J
Matt J 2019-1-8
编辑：Matt J 2019-1-8
Then, reshaped sq is 62005248*64, and w is 64*64. Since matlab uses double as default, it'll raise memory exceeding error when performing multiplication.
First of all, no, if you multiply a single matrix by a double matrix, the result will be a single matrix.
Secondly, the memory consumption that you've described doesn't add up. You said in your initial post that you had just enough memory to hold the repmatted sq, which was of dimensions [116 116 72 64 64]. That had to consume at least 4 GB. If you had enough memory for that, you should have plenty of memory to spare (now that you're not using repmat) to hold the original sq in single or even double format. In single format, this only consumes 0.25 GB:
>> whos sq
Name Size Kilobytes Class Attributes
sq 116x116x72x64 242208 single
If you're still getting out of memory errors, my suspicion is that you are still using repmat somewhere.
Zhixin Pan
Zhixin Pan 2019-1-8
Yes, you're correct.
Double multiplied by a single is still single.
And for sq in 116x116x72x64, even if we set it to double, it's still smaller than repmatted sq.
So it's kind of wield that matlab gave memory exceeding error on these 2 situation, I'll check it out.
But your solution is perfect, thanks, you saved my life.

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