preallocate array without initializing
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Is there any way to preallocate a matrix without initializing it to either NaN's, zeros or ones?
I'm working with large image data, typically 1-4 billion pixels, and need to preallocate the array so I can read the data in in chunks. I don't need the array initialized because I will either fill the entire array if reading the data is successful, or throw an exception if it fails.
Preallocating the array with either zeros or NaN's takes matlab several seconds to initialize the array.
Allocating a large array like this in C++ returns immediately because it neither new(...) or malloc(...) bother to initialize the memory.
Is it possible to allocate the array either in a C++ mex file or using coder.ceval(...) to avoid the initialization time?
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Steven Lord
2018년 11월 30일
If you want a matrix of class int16 filled with 0 elements, don't wrap a call to zeros in a call to int16. Instead use the typename input listed on the documentation page for the zeros function.
z = zeros(1e4, 1e5, 'int16');
Are you trying to read in a sequence of images that may take up more memory than you have avaialble (or a significant fraction of your available memory?) If so consider creating a tall array from an ImageDatastore and performing your analysis on the tall array. See this documentation page for more information on tall and datastore arrays.
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Walter Roberson
2018년 12월 2일
Some history . I have not found anything definitive as to when Demand Zero was introduced . Demand paging dates to 1961.
Demand Zero requires MMU which were not present in the intel 80* series until the 80286
https://sigops.org/sosp/sosp15/history/04-satya-slides.pdf
https://homes.cs.washington.edu/~arvind/cs422/lectureNotes/l16-2.pdf
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Bruno Luong
2018년 11월 30일
편집: Bruno Luong
2018년 11월 30일
MEX can do that, use for example this utility
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per isakson
2018년 11월 30일
편집: per isakson
2018년 11월 30일
Try this
>> A(100,100) = 0;
>> whos A
Name Size Bytes Class Attributes
A 100x100 80000 double
I believe it is described by UndocumentedMatlab, but don't find it now. However, see the two first comments to the blog piece, which I linked to.
Maybe, more relevant
>> B(100,100)=uint8(0);
>> whos B
Name Size Bytes Class Attributes
B 100x100 10000 uint8
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