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QRDecomposiiton difference between 12.0 and 12.3

Posted 4 months ago
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I happened to find a huge difference in QRDecomposition between 12.0 and 12.3. The QR decomposition of the sparse array in the following notebook file finishes less than a second on 12.0.

However, it gives a warning on 12.3: N: internal precision limit MaxExtraPrecision=50.` reached while evaluating. enter image description here Showing the stack track tells that the Mathematica is getting the Sign of this number, which is actually 0 after simplification. Is there any way to get rid of this internal numerical simplification?

I wish someone can fix this issue in future release.

3 Replies

Thanks for the example. I'll take a look.

To confirm, the algorithm for the exact/symbolic case did change in version 12.3. But the intent was not to degrade performance.

Hi, Thanks very much for your quick reply, I wish the result to be symbolic, it is constructed from some structure constants of SU(3) group, it is expected to be nice symbolic forms

I would guess this is not in the QRDecomposition part but rather in some simplification algorithm it uses internally to simplify expressions. Do you need the result to be symbolic? Because you're pushing the limits I think with doing QR decomposition with quite big symbolic matrices…

EDIT: I was wrong; but good for Daniel to look into :-)

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