Desired object produced but still receive "out of memory error"

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I encountered something quite odd and was hoping someone could provide some insight.
I have a very large variable ("W") that I need to run through some logical indexing in the form of a for loop. The end result should be a 110000 X 5000 X 401 3D matrix, but 220.5 billion numbers is a bit much for memory to handle, even if I make it a sparse array. You can see I've broken "W" up into 11 parts to see if that works.
This code ran for me and produced the object "b_1", but I still got an out of memory error. The out of memory error suggests to me that the object should have never been produced. I'm not sure that I trust the produced object "b_1" because of the out of memory error. Am I being too paranoid, or would it be wise to look for a different solution?
T = 5000
W = zeros(110000, 5000);
for trial = 1:T
X2ri = X;
X2ri(10001:20000, 46:50) = randi([1,5], 10000, 5);
X3ri = X2ri;
X3ri(20001:30000, 41:50) = randi([1,5], 10000, 10);
X4ri = X3ri;
X4ri(30001:40000, 36:50) = randi([1,5], 10000, 15);
X5ri = X4ri;
X5ri(40001:50000, 31:50) = randi([1,5], 10000, 20);
X6ri = X5ri;
X6ri(50001:60000, 26:50) = randi([1,5], 10000, 25);
X7ri = X6ri;
X7ri(60001:70000, 21:50) = randi([1,5], 10000, 30);
X8ri = X7ri;
X8ri(70001:80000, 16:50) = randi([1,5], 10000, 35);
X9ri = X8ri;
X9ri(80001:90000, 11:50) = randi([1,5], 10000, 40);
X10ri = X9ri;
X10ri(90001:100000, 6:50) = randi([1,5], 10000, 45);
X11ri = X10ri;
X11ri(100001:110000, 1:50) = randi([1,5], 10000, 50);
XFri = X11ri;
W(:,trial) = var(XFri,0,2);
W_1 = W(1:10000,:);
W_2 = W(10001:20000,:);
W_3 = W(20001:30000,:);
W_4 = W(30001:40000,:);
W_5 = W(40001:50000,:);
W_6 = W(50001:60000,:);
W_7 = W(60001:70000,:);
W_8 = W(70001:80000,:);
W_9 = W(80001:90000,:);
W_10 = W(90001:100000,:);
W_11 = W(100001:110000,:);
varinc = (0:0.01:4);
b_1 =[10000,5000,401]);
for i = 1:length(varinc)
b_1(:,:,i) = W_1 >= varinc(i);

Accepted Answer

Walter Roberson
Walter Roberson on 26 Sep 2020
you are using
You need to use nzmax to preallocate the object. Otherwise every time you assign into the object, matlab needs to create a copy of the array with one more value slot and copy the old one over.
Hi Walter,
Thank you again for your insight! This has given me a lot to think about, but it will make my future code much better.

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