How do I make a lower triangular matrix from a column vector?
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I am trying to make a lower triangular matrix from a column vector to then produce a fully populated 24x24 symmetric matrix.
The column vector I'm using (A as a simple example) has 300 elements and I need to populate the triangular matrix (B as a simple example) as follows:
A = [i1 i2 i3 i4 i5 i6 i7 i8 i9 i10 ...]
B = [i1; i2 i3; i4 i5 i6; i7 i8 i9 i10; ....]
Any help would be appreciated. It may be that it's easier to make the symmetric matrix straight away, if so I'm open to suggestions. Thanks in advance.
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Rik
2021 年 3 月 9 日
The functions you should be looking for are tril and triu. You should be using triu, because you seem to want to fill your array in row-major order, while the Matlab default is column-major.
A=1:21;%replace with your data
%sz will only be a positive integer if numel(A) is a triangle number
sz=-0.5+sqrt(0.25-4*0.5*-numel(A));
B=triu(ones(sz));
B(logical(B))=A;
B=B.';
disp(B)
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Rik
2021 年 3 月 29 日
Similar to Jan, my Python skill are only rudimentary. If you are an actual Python user, your success in googling documentation will probably be higher.
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