I have a 300 x 150 zeros matrix and want to change only the lower triangular elements to 1, How do I do that?

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Daniel Gray
Daniel Gray 2017-7-3
编辑： Image Analyst 2024-3-17
Everything is in the title really, I need to change the lower triangular elements of this zeros matrix to 1, how can I do this easily?

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Image Analyst
Image Analyst 2017-7-3
编辑：Image Analyst 2024-3-17
Ran in:
You don't even need your original zeros matrix (let's say you called your original matrix "z") since it gets completely overwritten by 0's and 1's.
Simply make a 300 x 150 matrix of zeros with the lower left triangle of 1's like this:
z = [zeros(150); tril(ones(150), 0)];
% Now verify and display it.
size(z)
ans = 1×2
300 150
imshow(z)
axis('on', 'image')

更多回答（3 个）

KSSV
KSSV 2017-7-3
编辑：KSSV 2017-7-3
idx = ones(300,150) ;
idx = tril(idx,1) ; % Make 1's at lower triangular part
A = rand(300,150) ; % given matrix
A(idx==1) = 1 ; % replace lower triangular part with 1
Jan
Jan 2017-7-3
编辑：Jan 2017-7-3
In Matlb >= R2016b:
M = (1:300).' >= (1:150);
For older Matlab versions:
M = bsxfun(@ge, (1:300).', 1:150);
Abdurayimov Orzumurod
idx = bir (300,150);
idx = tril(idx,1) ; % Pastki uchburchak qismiga 1 qo'ying
A = rand (300,150); % berilgan matritsa
A(idx==1) = 1 ; % pastki uchburchak qismini 1 bilan almashtiring

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