P3371R3: LEWG presentation 2024/11/22

[mhoemmen]

P3371R3: Fix C++26 by making the rank-1, rank-2, rank-k, and rank-2k updates consistent with the BLAS

Background

Definitions

• Conjugate: If $z = x + i y$, $\bar{z} = x - i y$
• Transpose:
  • If $x$ is a column vector, $x^T$ is a row vector, and vice versa
  • $A^T$ is the matrix $B$ with $B{cr} = A{rc}$
• Hermitian transpose: $A^H = {\bar{A}}^T
• Symmetric matrix: $A{rc} = A{cr}$
• Hermitian matrix: $A{rc} = \bar{A{cr}}$

Rank-1 updates

• rank-1 update: $A$ -> $\beta A + \alpha x y^T$
• symmetric rank-1 update: $A$ -> $\beta A + \alpha x x^T$
• Hermitian rank-1 update: $A$ -> $\beta A + \alpha x x^H$

Rank-2 updates

• symmetric rank-2 update: $A$ -> $\beta A + \alpha x y^T + \alpha y^T x$
• Hermitian rank-2 update: $A$ -> $\beta A + \alpha x y^T + \alpha y^T x$

[mhoemmen]

I've replaced this with a proper set of slides.