[FluidKo]

Hello everybody~!

I was wondering what is initial residual and final residual.
So I've searched these things in CFD Online and Youtube.
I've seen video at below link.
https://www.youtube.com/watch?v=OOILoJ1zuiw&t=1s
And I've found this post
SIMPLE: Difference between initial and final residuals

At upper link, 'Zbynek' has said that
"When your final residual is low enough, you update the matrix and repeat the whole process I just described (called outer iteration). Voila, you get a new initial residual that has naturally a larger value than the previous final residual."

I'm wondering two points.

1. Deos 'Ax=b' means Navier-Stokes equation?
https://youtu.be/OOILoJ1zuiw?t=281
At this link, is representing Navier-Stokes equation. So I've thought 'Ax=b' that Zbynek is referring is meaning Navier-Stokes equation and same to .
Is it right?

2. If 'Ax=b' means Navier-Stokes equation, then how A can be updated during outer iteration?
What I've guessed is below.
At below link,
https://youtu.be/OOILoJ1zuiw?t=360
can be transformed into .
And this means can be expressed like below link.
https://youtu.be/OOILoJ1zuiw?t=410
Also means H can be changed by U.
Because H is changed by U and H is component of MU, if U is updated M must be changed.
And M is same thing to A in 'Ax=b'
Is it right? I'm not sure...
Eventhough we've updated only x then substitute it into ,
how M(same thing to A in 'Ax=b') can be updated?

Thank you~!