@acegikmo 's are just plural suffix.

x are variables in the middle matrix, that are now a

@dpwiz I'm confused lol, the matrix with all the 'a' is already aligned with the b matrix and the t matrix in terms of the coefficients in the polynomial, that's the point of the tweet

@acegikmo I'm talking about the variable names.
they can be position mnemonics so

the linear form would look like

l0 +
l1x0 + b l1 x1 +
....

This way one can easily sort them out to proper positions in the notation form and collect back to linear.

@dpwiz oooh right, sure lol

@acegikmo sorry for the confusion 😅

@acegikmo @dpwiz
s/a/x/ is line editor notation for replace "a" with 'x".
The g on the end s/a/x/g makes it global, replacing a with x throughout the document.

@zl2tod oh, I've never seen this notation before

@acegikmo
I'm going to have to read up on my matrix notation too.
There's an s// example here. Sorry.
https://en.wikipedia.org/wiki/Ed_(text_editor)

@acegikmo @zl2tod it's also commonly found in sed, a text processing command