Maximum array size in MATLAB?

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-上瘾入骨i
-上瘾入骨i 2021-01-02 22:15

I\'m writing a MATLAB program that will generate a matrix with 1 million rows and an unknown amount of columns (at max 1 million).

I tried pre-allocating this matrix

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  •  难免孤独
    2021-01-02 22:25

    The Limits

    There are two different limits to be aware of:

    1. Maximum array size (in terms of number of elements) allowed by MATLAB, regardless of current memory availability.
    2. Current bytes available for a single array -- the (current) maximum possible array size in bytes.

    The first limit is what causes "Maximum variable size allowed by the program is exceeded", not the second limit. However the second one is also a practical limit of which you must be aware!

    Checking the Limits

    The maximum number of elements allowed for an array is checked as follows:

    >> [~,maxsize] = computer
    maxsize =
       2.8147e+14
    

    According to the documentation for the computer command, this returns:

    maximum number of elements allowed in a matrix on this version of MATLAB

    This is a static MATLAB limit on number of elements, not affected by the state of the computer (hardware specs and current memory usage). And at over 2 petabytes for a double array of that length, it's also way higher than any computer of which I am aware!

    On the other hand, the largest practical array size that you can create at any given moment can be checked by the memory command:

    >> memory
    Maximum possible array:     35237 MB (3.695e+10 bytes) *
    Memory available for all arrays:     35237 MB (3.695e+10 bytes) *
    Memory used by MATLAB:      9545 MB (1.001e+10 bytes)
    Physical Memory (RAM):     24574 MB (2.577e+10 bytes)
    
    *  Limited by System Memory (physical + swap file) available.
    

    As the message says, these values are based on actual current memory availability, taking into account both physical memory and the swap file (collectively, virtual memory).

    If needed, these values can accessed programmatically by m = memory;.

    Adjusting the Limits

    The first limit (the hard limit) has been fixed up until R2015a, where it can now be changed (but only reduced to a fraction of system memory) through the following setting:

    enter image description here

    You can't increase it beyond your system limits.

    The second limit obviously has no "setting" in MATLAB since it's based on available memory and computer configuration. Aside from adding RAM, there's not a lot you can do: (1) pack to consolidate workspace memory and perform "garbage collection", but this may only help on certain platforms, and (2) increasing page file size to allow other stuff to swap out and give MATLAB more physical memory. But be cautious when relying on your page file as your computer may become unresponsive if page file thrashing happens.

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