public function getNEq_diffusive(layout, omega, Sxx) result(nEq)

Calculate the non-equilibrium part of pdf from strain rate tensor
based on the diffusive scaling

According to \cite Junk:2005cr \n
The non-equilibrium part of pdf is set by \n
where is the viscosity,
is the strain rate tensor and
and is the number of dimension. \n
Notice here that strain rate tensor above has to be a traceless tensor, i.e.
.
In current implementation,
the above equation is slightly modified so that
the strain rate tensor is not required to be traceless anymore.
In this way, calculated by this routine can recover the
input strain rate tensor no matter it is traceless or not.\n
Specificly the in above equation is modified slightly, i.e.
This routine has a unit test program utest/mus_fNeq_diffusive_test

Nodes of different colours represent the following:

Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.

Nodes of different colours represent the following:

Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.