how to convert from and to QR compact format?

[bravegag]

Hello,

Please note that I am new to LAPACK and fortran.

Can anyone please point me to documentation or functions on how to convert from explicit Q and R to compact LAPACK QR? I would like to make my explicit Q and R to the QR format produced by dgeqrf.

I think I know how to do the other way around, from the compact LAPACK QR format to Q is using dorgqr or dormqr and recovering the R would be using cblas_dtrsm multiplying by the identity, right?

I need this in the context of an iterative algorithm that mutates matrices in different ways and it is very relevant to efficiently update QR by columns and/or row modifications and this is not standard part of LAPACK and therefore the need I have to deal with the different representations.

Many thanks in advance,
Best regards,
Giovanni

[admin]

Yes this is correct.
See http://netlib.org/lapack/lug/node40.html and http://netlib.org/lapack/lug/node128.html#secorthog
Julie