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From Sean Owen <sro...@gmail.com>
Subject [MATH] How to handle QRDecomposition and a tall, skinny matrix (MATH-1053)?
Date Tue, 05 Nov 2013 14:12:58 GMT
For background, see https://issues.apache.org/jira/browse/MATH-1053

The issue is what to do when QRDecomposition is used on a tall, skinny
matrix (m rows > n cols), and getSolver().getInverse() is called.
Right now a DimensionMismatchException is thrown, which is almost
certainly not intended.

That first exception can be fixed, and in theory the QR decomposition
can produce an answer here. However I'm not sure how to complete the
fix, since I don't understand enough how the triangular system with R
is solved in terms of the block representation.

(Most ideally, someone could help fix that!)

But if not, at the least it seems desirable to throw a different and
more intentional exception in this case, for QRDecomposition only. Or
at the very least, document that DimensionMismatchException is
intended.

Comments invited, here or on the JIRA.

Sean

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