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using the project function to find gradients perpendicular to a boundary

To: dolfin <dolfin-dev@xxxxxxxxxx>
From: phil marinier <lonewolf_13p@xxxxxxxxxxx>
Date: Sun, 12 Jul 2009 12:23:03 -0400
Delivered-to: dolfin-dev@xxxxxxxxxx
Importance: Normal

I am trying to find the gradients perpendicular to a boundary. The way I think I want to do this is by using the w = grad(u) function in my python code to get the gradients, and then use perpGrad = project(w, V) somehow to get the perpendicular gradients. I can't find any documentation for the project() function and so far have not found any examples using it. I assume that V is a function space and the project() function projects the first argument onto that function space. If so, is it possible to somehow make a perpendicular space onto which I can project my gradients? If not, is there another way to do this?
The boundary will always be a straight line and the domain is always rectangular. 
Thank you for your help