# convPrePost Function

## public pure function convPrePost(omega) result(conv)

Conversion factor betwen the pre- and post-collision quantity for the shear stress.

Shear stress calculation requires the non-equilibirium value of pdf before collision. However that value not may be accessable directly when PULL scheme is uitilized, as only pdf after collision is available. So this conversion factor is introduced to help recover fNeq before collision from fNeq after collision as long as relaxation parameter (omage) does not equal to 1.0. When omage equals to 1, this conversion factor is set to be 0.

How to use this pre-factor?

  shearstress = convPrePost(omega) * omega * cs2inv * shearLB_postColl


### Arguments

TypeIntentOptionalAttributesName
real(kind=rk), intent(in) :: omega

None