Hi Abhishek,

You can try the following approach:
1. Have a 2D solution with u,v,c,p.
2. Prepare a session file with NumSteps = 0, and a homogeneous
expansion in the z direction.
3. Add w to the expansion, variables boundary, etc. In initial
conditions read u, v, c, p from file and set w to zero.
4. Run it, and you get a solution with u,v,w,c,p.

Note: I am not sure you can successfully do this with HalfMode.
SingleMode will work.

Note 2: I am not sure this will be usable for the stability solver as
baseflow (although I see no reason why?). I have not used the stability
solver with an "active" scalar. I just played with the Rayleigh-Benard
problem after David Moxley activated the ability to formulate BodyForce
using the scalar value, about a year ago.

Best,
Stan

On pią, 2018-10-26 at 11:31 +0100, Abhishek Kumar wrote:
> Hi Stanislaw,
>
> Thanks for the prompt reply.
>
> 1) Yes, you are correct. There is no effect of HomModesZ. It gives
> the same result with HomModesZ=1.
> 2) For the base flow, it works with  <F VAR="u,v,p" FILE="bflow.fld"
> />. It doesn't ask for w.
>
> But the problem comes when we add a scalar variable (for a problem
> like Rayleigh-Benard). In this case, I use
> <F VAR="u,v,c,p" FILE="base.fld" />, and it gives the following
> error:
>
> Fatal   : Level 0 assertion violation
> For half mode, expect 2D2C base flow.
>
> I attached the session file. Can you comment on this issue?
>
> With regards
> Abhishek
>
>
> On Fri, Oct 26, 2018 at 8:29 AM Stanisław Gepner <
> sgepner@meil.pw.edu.pl> wrote:
> > Hi Abhishek,
> >
> > Have you tried with setting this value to 1, and did the solver
> > work
> > and returned the same result?
> >
> > 1. Anyway, as far as I understand what is in
> > SolverUtils/EquationSystem.cpp the value of HomModesZ is
> > overwritten on
> > initialization: 2 for SingleMode and 1 for HalfMode - so the value
> > in
> > the session file would seem redundant (Solver starts with this
> > value
> > removed).
> >
> > 2. Yes, AFAIK you need to have w in the BaseFlow section. It does
> > not
> > need to come from a file, you could do sth. like this:
> >
> > <F VAR="u,v,p" FILE="bflow.fld" />
> > <E VAR="w" VALUE="0" />
> >
> > So you can use a 2D solution with Fourier expansion.
> >
> > Best,
> > Stan Gepner
> >
> >
> >
> > On czw, 2018-10-25 at 22:31 +0100, Abhishek Kumar wrote:
> > > Hi,
> > >
> > > I am trying to understand the session file
> > "PPF_R15000_3D_VCS.xml." I
> > > have two confusion:
> > > 1) Since modeType is HalfMode than why "HomModesZ" is set to 2. I
> > > think this should be 1.
> > >
> > > 2) Since the base flow is 2D2C, then is it necessary to include
> > > variable "w" in the base flow?
> > >
> > > In general, can we use a base flow generated from DNS which only
> > have
> > > variables (uvp) in the session file having FIELDS =  (uvwp)?
> > >
> > > I would be highly thankful for the comments on this issue.
> > >
> > > With regards
> > > Abhishek Kumar
> > >
> > > ---------------------------------------------------------------
> > ----
> > > --------------------
> > > Abhishek Kumar
> > > Research Associate
> > > Applied Mathematics Research Centre
> > > Coventry University, Coventry CV1 5FB
> > > The United Kingdom
> > >
> > > Email # ac7600@coventry.ac.uk, abhishek.kir@gmail.com
> > > ---------------------------------------------------------------
> > ----
> > > --------------------
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>