[petsc-users] sequential Vec question

[Zou (Non-US), Ling]

Hi All,

For a 1-D problem with multiple variables (u, v, w), it is natural to put
those unknowns in a Vec for SNES to solve, like,

u0, v0, w0, u1, v1, w1, ... uN, vN, wN

as it would reduce the band width of the Jacobian matrix.

When passing this kind of structure to FormFunction, it is however not
convenient to access values as you need to jump around to get u(i-1), u(i)
and u(i+1). It is more convenient to have the structure in an order like

u0, u1, ... uN, v0, v1, ... vN, w0, w1, ... wN

Thus I need some way to map b/w them. I looked at the manual, it seems that
AO is probably the thing I am looking for. However, there are no specific
examples for them. I also tried VecScatter, split the original Vec to three
Vec(s), however, I am not quite sure if it is the right concept to use for
this kind of scenario.

Does anyone have experience on this topic (I bet it is quite common).


Best,

Ling
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