How much data does an array take?

2023 11 4
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My question is pretty much entirely in the title. I am curious about how matlab stores data and specifically how much data an nxn array takes to store. Is each element of the array an individual 8 byte double so the size is 8*n^2 bytes?

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James Tursa
James Tursa 2023-11-4
编辑：James Tursa 2023-11-4

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The data is held in contiguous memory, so yes for a full real double an NxN matrix would take 8*N^2 bytes for the data. Then there is a variable header that contains info such as class, dimensions, data pointers, etc. That takes an additional 132(?) bytes or so per variable. The actual header amount can vary from release to release, and I haven't checked lately what it is currently.

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Alec Bledsoe
Alec Bledsoe 2023-11-4
Okay. Just making sure I understand this, if I were to create an array A, where A = randi([0 9], n), I would get a variable that takes up 8*n^2+132 bytes?
James Tursa
James Tursa 2023-11-4
Ran in:
Ran in:
Yes, but the header amount doesn't show up under whos even though it is there. E.g.,
n = 10;
A = randi([0 9], n);
whos
Name Size Bytes Class Attributes A 10x10 800 double cmdout 1x33 66 char n 1x1 8 double
Alec Bledsoe
Alec Bledsoe 2023-11-4
Got it thank you. How do I check the header size?
Walter Roberson
Walter Roberson 2023-11-4
https://www.mathworks.com/matlabcentral/answers/2010767-struct-function-in-matlab
My answer there analyzes struct.
96 bytes to describe a variable. 8 bytes pointer to the data. Another 64 bytes to hold the variable name.

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