What does $b^*$ mean?

Question

What is this notation, my book explains nothing of it. I've colored it in yellow!

I am guessing it stands for $b^{-1}$ or $b^1$?

Answer 1

Usually $b^*$ is the complex conjugate of $b$. That is, if $b_{j}=x+iy$, then $b_{j}^{*}=x-iy$ (with $b\in\mathbb{C}^{n\times 1}$ and $b^*\in\mathbb{C}^{1\times n}$). In this context it seems like the author is just trying to use two different symbols. Ideally, you should not use this notation for anything other than complex conjugates in linalg.