Dear Paul,

Thank you for answering so quickly. Yes, the polynomial spaces I'm using are the standard Nek5000 basis functions.

To understand the problem a little better:

I am conducting DNS of a shear flow and I need to compute higher-order velocity moments. I've implemented some subroutines based on the "avg2" and "avg3" subroutines from Nek, but for higher order moments, i.e. <U^3>, <U^2 V>, etc. The problem is that I need to de-alias the non-linear quantities, i.e. U^3, before doing the averaging. Since the flow is planar, I also take the spanwise average using the "z_average" subroutine.

I checked out the "convect.f" file to see how dealiasing is applied by mapping onto the finer grid (lxd), but I'm not quite sure how to project these results back onto the original grid.

Thank you,

Juan Diego