Cleanup findInitialBasic and initializeFromBasic

[btracey]

No description provided.

[btracey]

PTAL @sbinet

[sbinet]

this is probably just very nit-picking but I would probably reverse the if-else-branch:

if !set {
   set = true
   extractColumns(ab, A, newBasic)
} else {
   mat64.Col(col, i, A)
   ab.SetCol(addedIdx, col)
}

that way, the test on set and its first (and last) modification are closer, visually.

(when I read it first, I was a bit confused whether this wasn't just dead code...)

[btracey]

Done.

[btracey]

Actually, I accidentally nuked my local version of this... I'll submit this in the next PR

[sbinet]

just a little nitpick, but LGTM otherwise.