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Azua_Garcia__Giovann

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04-18-2012
06:56 PM

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dormqr trick?

I couldn't figure out from the documentation how to achieve the following use-case.

I have a matrix A for which I compute its QR factorization using geqrf. For some sound reasons (I need you to trust me here so the story is short) I need to apply Q to a c vector but with an identity appended to the bottom of the Q and using dormqr. I do this by appending a row of zeros to my compact QR decomposition and a zero element to my tau vector and this works fine.

Now I would like to accomplish the same with dormqr but without having to use this artifact that pollutes my QR with an extra row of zero. How can I do that? I have searched all over but can't find the solution unless I give up with dormqr and loop over and invoke dlarf.

The problem is that the appending a row of zeros to my QR in column-major is very expensive and sort of defeats the gain I get by doing QR updates (this is the reason).

Many thanks in advance,

Best regards,

Giovanni

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Azua_Garcia__Giovann

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04-20-2012
03:23 AM

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