Re: Overwriting 41C module internals Message #11 Posted by spb on 29 Apr 2011, 9:31 p.m., in response to message #10 by 聲gel Martin
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Well, any singular Matrix (with Det=0) will yield the same absurd result since it won't be invertible. That's why I asked before if det#0 as a condition.
Is this true on a working Advantage module? I would've expected it, like for example the 15C, to `invert' [[0, 0], [0, 0]] to [[10e99, 0], [0, 10e99]] as an artefact of the numerical algorithm used (and the limits of the machine itself). This is what the Advantage module I have gives if the matrix is inverted immediately after entering. Inverting again gives [[10e99, 0], [0, 10e99]], again matching the behaviour of the 15C. Attempting to do the same thing following taking the determinant gives the nonsensical result.
In any case it gives a similarly nonsensical result for [[1, 2], [3, 4]]. Specifically, inverting and reinverting after taking the determinate does not give the original matrix, but rather apparently arbitrary values in the diagonal elements.
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It's highly unlikely (albeit of course possible) that there's such an issue in the module, affecting just one function  that's what made me suspicious in the first place.
I don't know if it's only in one function; I've only seen problems with one function, but I haven't attempted to manually check every function in the module. It's even possible that there are different errors in, for example, the solver used by MATRX as well as MDET. I was just assuming that the solver called MDET internally and so the problem with MDET explained the spurious results given by the solver.
