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dgebd2 routine: 3rd parameter passed to dlarfdg is an array?

PostPosted: Thu May 04, 2017 7:19 am
by marcoi
Hi,
I'm trying to understand the inner functioning of dgebd2 routine
What I do not understand is the third parameter passed to dlarfdg routine : https://github.com/Reference-LAPACK/lapack/blob/master/SRC/dgebd2.f#L245
The third parameter, as far as I understood, should be an array: https://github.com/Reference-LAPACK/lapack/blob/master/SRC/dlarfg.f#L107
but....is A( MIN( I+1, M ), I ) an array?

Looking forward to your kind explanations and hints.
Marco

Re: dgebd2 routine: 3rd parameter passed to dlarfdg is an ar

PostPosted: Mon May 15, 2017 6:15 am
by Julien Langou
Hi Marco.

(1) Before looking at DGEBD2, please look at DGEQR2 then. This will help you understand the behavior of DLARFG. This is easier to understand, I believe.

(2) A( MIN( I+1, M ), I ) points to the start of the array. Yes it represents an array. Its start. Please look at the interface of DLARFG as well.

If you are more comfortable with C++, please have a look at:
https://github.com/langou/latl/blob/master/include/geqr2.h

Julien.