MATLAB: How matlab stores graphics objects

dataMATLAB

when i create a figure i noticed that it have alot of propeties and each property hold values,

that means alot of bytes, but the figure size seems to be 8 bytes despite all the properties values which are having a greater size,

my question is if properties values are not stored on (RAM), then where the properties values are stored then, and how matlab calls them that fast if they are really not stored on RAM.

please don't give me links, and thanks in advance

Best Answer

The Bytes column of the output of whos does not tell the "truth, whole truth, and nothing but the truth" for certain situations.

A = zeros(100);
B = A;
whos A B
  Name        Size             Bytes  Class     Attributes

  A         100x100            80000  double              
  B         100x100            80000  double

A and B do not necessarily point to a different block of 80,000 bytes due to the copy-on-write behavior of MATLAB.

f = figure;
whos f
  Name      Size            Bytes  Class               Attributes

  f         1x1                 8  matlab.ui.Figure

This does not list the full amount of memory required to store all the data and properties associated with a figure window.

Use that data as guidance, not law.

And no, there is no way to get the actual amount of memory associated with f (maybe walking the list of properties in a MEX-file, but again things like copy-on-write would complicate even that.)

Related Solutions

MATLAB: How the command whos works

This memory corresponds exactly to the quantity in bytes given by the command whos.

However you have to add to that the header size to hold information about the variable.

>> abc = 0
abc =
     0
>> whos abc
  Name      Size            Bytes  Class     Attributes
  abc       1x1                 8  double

abc is a double precision variable with one entry, and each double precision value needs 8 bytes. 1 row * 1 column * 8 bytes per entry = 8 bytes.

But storage is also occupied to hold the information that abc is 1 x 1, and that it is class double, and that it is not complex-valued, and that it is not global. whos does not report about that space.

MATLAB: How to find the amount of data generated/memory requirment for a program

Sorry. It is not possible to do these things in general.

MATLAB uses dynamically generated variables and arrays. So the memory required can easily vary according to the inputs of your function. And since temporary variables will be created by functions that are called, they may be arbitrarily large.

Suppose you have a function that calls a function. Down in the depths of one of these sub-functions, it sometimes chooses to call the function perms(1:1000), based perhaps on something unknowable. Or worse, suppose you have code that looks like this:

n = input('what is n?')
str = ['A = perms(1:',num2str(n),');'];
eval(str)

Yes, I know, obscene code. But if someone types in 1000 to that question, the result will be something that will take more space than any computer would have in this universe, even if every single elementary particle in the universe was a byte of RAM. Worse, MATLAB cannot know in advance this would happen. So it cannot look at that code without evaluating it to know ho much memory will be required.

Best Answer

Related Solutions

MATLAB: How the command whos works

MATLAB: How to find the amount of data generated/memory requirment for a program

Related Question