How much data does an array take?

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?

Answer 1

[James Tursa]

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.

[Alec Bledsoe]

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]

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]

Got it thank you. How do I check the header size?

[Walter Roberson]

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.