[Nek5000-users] Linearized Nek: Compute only the right-hand side

[nek5000-users at lists.mcs.anl.gov]

Hi Nek's,

Given a random initial vector u and the Jacobian matrix of the linearized
Navier-Stokes, I would like to calculate the matrix-vector product J * u. In
Nek, that would consists in calculating only the right hand side of the
equations, that is:

RHS = ( -U.grad(u) - u.grad(U) - grad(p) + 1/Re Lap(u)    ;    div(u) )

I have a few questions on how to compute those different terms in userchk
(Nek is used in post-process mode):

   - I would tend to use convop() for the convection terms, however I'm not
   sure whereas it would output the strong or weak form (and I need the strong
   one obviously)?
   - Same question regarding grad(p) and div(u) if I use opgradt() and
   opdiv() to calculate them?

Last but not least, for the Laplacian I've read a previous mail where it is
said that it can be computed using a sequence of wgradm1() and vec_dssum()
so I guess I kown how to compute at the strong form for it.

Sincerely,
-- 
Jean-Christophe
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