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serious inverse matrix bug?
12-05-2019, 04:49 AM
Post: #1
serious inverse matrix bug?
Hello, I found this bug calculating the inverse of a matrix in the latest firmware, Have you guys seen it in any previous firmware before?

[Image: error_inversa%20prime_01.jpg]
[Image: error_inversa%20prime_00.jpg]

[Image: error_inversa%20prime_02.jpg]
[Image: error_inversa%20prime_03.jpg]
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12-05-2019, 01:16 PM
Post: #2
RE: serious inverse matrix bug?
I forwarded on to the CAS author and it has been corrected. Only looked like it happened due to the approximate number in there.

1/2*s would have worked fine.

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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12-05-2019, 01:38 PM (This post was last modified: 12-05-2019 01:48 PM by Albert Chan.)
Post: #3
RE: serious inverse matrix bug?
Tried doing inverse by "hand", XCas 1.4.9-57 (win32).
The bug maybe in rref()

Code:
XCas> m := [[1,0,1,0], [0,1/(2*s),0,1]]
XCas> rref(m)          → [[1,0,  1,0]    , [0,1,  0,2*s]]
XCas> rref(float(m))   → [[1,0,  2.0*s,0], [0,1,  0,4.0*s^2]] ???

BTW, doing inv([[1,0], [0,1/(2.*s)]]) crash XCas.
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12-05-2019, 07:10 PM
Post: #4
RE: serious inverse matrix bug?
(12-05-2019 01:38 PM)Albert Chan Wrote:  The bug maybe in rref()

Yes, it was a bug in rref. I fixed it by converting approx coefficients to exact (with a warning).
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