[Matlab Grader] How to check if the matrix has upper triangular form?

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Biljana Gjeroska
Biljana Gjeroska 2020-12-21
评论： Biljana Gjeroska 2020-12-21
Hi,
I want to build a test that checks if a matrix has an upper triangular form. But somehow it didn't work in Matlab Grader.
I tried to use the matlab function istriu
A = [1.6537 1.1405 1.2570;
0.0000 0.9661 0.6341;
-0.0000 0.0000 0.8816;
-0.0000 -0.0000 -0.0000;
-0.0000 0.0000 0]
isUpper = istriu(A)
but it gives me always zero back, even though the matrix is upper triangular. When I am doing it locally, it gives me the right answer.
Does someone know why is this happening and how can I solve it?

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James Tursa
James Tursa 2020-12-21
编辑：James Tursa 2020-12-21
This looks like a display issue. The numbers in the lower triangle are not exactly zero, they just display that way out to 4 digits. Take a look at this result:
A == 0
and you will likely see that some of those lower triangular elements are not exactly 0.
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Biljana Gjeroska
Biljana Gjeroska 2020-12-21
Thanks a lot. I was thinking that the numerical deviation is already taken into account. But here I need to build it manually :)

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