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[Octave-bug-tracker] [bug #60797] sqrtm: returns nan for matrix of ones
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From: |
Markus Mützel |
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Subject: |
[Octave-bug-tracker] [bug #60797] sqrtm: returns nan for matrix of ones with rows and columns >=4 |
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Date: |
Mon, 6 Dec 2021 13:17:10 -0500 (EST) |
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User-agent: |
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.55 Safari/537.36 Edg/96.0.1054.43 |
Follow-up Comment #5, bug #60797 (project octave):
Installed the version from octave.space here.
It fails like this:
>> sqrtm(ones(4))
warning: sqrtm: matrix is singular, may not have a square root
ans =
0.500000 0.500000 0.024457 0.975543
0.500000 0.500000 0.658514 0.341486
0.500000 0.500000 0.658514 0.341486
0.500000 0.500000 0.658514 0.341486
Seems to be a pretty good solution though:
>> ans^2
ans =
1 1 1 1
1 1 1 1
1 1 1 1
1 1 1 1
The 64-bit version calculates the expected solution:
>> sqrtm(ones(4))
warning: sqrtm: matrix is singular, may not have a square root
ans =
0.5000 + 0.0000i 0.5000 - 0.0000i 0.5000 - 0.0000i 0.5000 - 0.0000i
0.5000 - 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i
0.5000 - 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i
0.5000 - 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i 0.5000 + 0.0000i
Do we expect that this function returns the same value on all platforms for
this test?
Or should we just change the test to something like:
assert (sqrtm (ones (4))^2, ones (4), 4*eps)
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