### Subroutine question: DLARFX

Posted:

**Wed Mar 22, 2006 3:33 am**Hello.

My question:

I am looking over the code for DLARFX. The purpose state the following: DLARFX applying a real elementary reflector H to a real m by n matrix C, from either the left or the right. H is represented in the form: H = I - tau * v * v', where tau is a real scalar and v is a real vector. If tau = 0, then H is taken to be the unit matrix.

I have no idea about the term "elementary reflector" and the background knowledge. Somebody please clarify for me.

Ps. Actually, I was asked to optimize this routine. It would be highlyappreciated if someone could give me some recommendations or approaches.

Thanks a lot.

My question:

I am looking over the code for DLARFX. The purpose state the following: DLARFX applying a real elementary reflector H to a real m by n matrix C, from either the left or the right. H is represented in the form: H = I - tau * v * v', where tau is a real scalar and v is a real vector. If tau = 0, then H is taken to be the unit matrix.

I have no idea about the term "elementary reflector" and the background knowledge. Somebody please clarify for me.

Ps. Actually, I was asked to optimize this routine. It would be highlyappreciated if someone could give me some recommendations or approaches.

Thanks a lot.