Preallocating cells with unknown output size

조회 수: 4 (최근 30일)
Joel Schelander
Joel Schelander 2021년 4월 12일
댓글: Bruno Luong 2021년 4월 12일
I need to optimize my script. A thing I could do is preallocating, however the size of my output cell is unknown so my question is if it is worth it.
the output of the script is X, the size of X is not known.
Now I have:
X={};
*my script
X=nxn cell
If the output cell has the size 2x2 for example, can I do something like this:
not sure if it will increase the speed of my script
X=cell(999);
*my script
X=999x999 cell
*somehow reduce the size of X
X=2x2 cell
  댓글 수: 5
Joel Schelander
Joel Schelander 2021년 4월 12일
The size of X will increase to the magnitude 100 million I think. Right now Im just working with a very small sample to optimize the script.
Bruno Luong
Bruno Luong 2021년 4월 12일
10 millions by 10 million cell?
I don't believe any existing HW can support that at the moment.

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Bruno Luong
Bruno Luong 2021년 4월 12일
편집: Bruno Luong 2021년 4월 12일
If the size is not known, a good way is the to grow the preallocation array exponentially.
Rather than the assigment
X{i,j} = value;
Call
X = gassign(X,i,j,value);
where gassign implemented as follow
function X = gassign(X, i, j, val)
[m,n] = size(X);
if (i > m) || (j > n)
gidx = @(s,k) max(max(2*s,s+1),k);
X(gidx(m,i),gidx(n,j)) = {[]};
end
X{i,j} = val;
end
Then when finish truncate X to remove not filled cells.
You can start the script with X initialized as
X = {};

추가 답변 (1개)

KSSV
KSSV 2021년 4월 12일
You can try to initilize them as
X = cell([],[]) ;
You can check the timing using tic , toc.

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