why it will go wrong using 'cell'?

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warnerchang
warnerchang 2022-3-31
评论： warnerchang 2022-4-1
Recently, I ran two codes as follow:
a={[],[]};a{1}(a{1}==3)=[];
% it will go wrong
b=cell(1,2);b{1}(b{1}==3)=[];
  2 个评论
KSSV
KSSV 2022-3-31
Ran in:
The difference is the space allocated for each.
a={[],[]};
b=cell(1,2);
whos a b
Name Size Bytes Class Attributes a 1x2 208 cell b 1x2 16 cell
warnerchang
warnerchang 2022-3-31
however，what happened behind cell function? As far as I know, a = {[],[]} and b = cell(1,2) should get the same result.

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采纳的回答

Jan
Jan 2022-3-31
编辑：Jan 2022-3-31
Ran in:
I confirm, that this is an inconsistent behavior.
a = {[], []};
b = cell(1, 2);
isequal(a, b)
ans = logical
1
a{1}([]) = [] % Working: Nothing is deleted as expected
a = 1×2 cell array
{0×0 double} {0×0 double}
b{1}([]) = [] % Failing:
Deletion requires an existing variable.
Both methods create a cell array of the same size, but cell() fills the elements with a NULL pointers, while {[], []} creates empty matrices. Matlab should treat NULL pointers as empty matrices, but as you see in this example, this exception has been forgotten sometimes. You cannot detect the NULL points from inside Matlab, but on the C level this is easy. KSSV's method to check the used memory is a strong hint also.
Report this bug to MathWorks. The function for deleting will be updated than to catch this exception.

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