Restart from a linear combination

[marinamartinf]

Hello,

I'm new to NekRS and I would like to ask if it's possible to perform a restart from a linear combination of two previous solution fields.

I've seen in the documentation that it's possible to initialize a run using fields from different .fld files, selecting which field to use from each file. However, I haven't found any mention of the possibility of computing a linear combination of the same fields from two different solution files as the initial condition.

Is this functionality currently supported in NekRS, or would it require a custom implementation?

Any help would be appreciated.

Thank you in advance.

[joneuhauser]

On master, you could do:

platform->options.setArgs("RESTART FILE NAME", "input1.fld");
nek::setic();
nek::copyFromNek(curtime);

You now have the data in nrs->U, nrs->p and nrs->cds->S.
Allocate a temporary helper array on the device (platform->device.malloc) where you copy the data to, slice it for U, p, and S.

Repeat with the second field, but this time do nek::ocopyFromNek(curtime), the data is now in the correct target arrays.

Run platform->linalg.axpby to compute the linear combination. The result will be in the device arrays.

On next, you have direct access to the read methods in iofld so you don't have to do the hack with setting the restart filename.

[yslan]

For the next and v24-development, you can follow the ethier's CI test like this:

nekRS/examples/ethier/ci.inc

Line 743 in 5152fec

nrs->restartFromFile(restartFile);