I am trying to initialize my PDF fields as shown in Skordos 1993[/url] and [url=http://www.springerlink.com/content/p832u0u402761261/]Caiazzo 2005, with the correct shear rates.

In particular I am trying to recreate the Taylor-Green vortex presented as a test case for initial conditions in Skordos '93.

However, my errors are not decreasing as they should. In fact I get larger errors than with the pure equilibrium initialization.

I wrote a D2Q9 Matlab code, and the perturbation from the shear stresses is calculated by a function,

```
function [f1] = CalcFirstOrderPerturbation(dxux, dxuy, dyux, dyuy)
for dir=1:9
f1(:,:,dir) = -tau*3*weight(dir) * ...
(cx(dir)^2 * dxux + cy(dir)^2 * dyuy + ...
cx(dir)*cy(dir)*(dxuy + dyux) );
end
end
```

where dxux is the partial derivative d[sub]x[/sub]u[sub]x[/sub] and so onâ€¦

The function was working great in a 2D-Couette Flow where you have only dyux and all other derivatives vanish. In this more complicated case it does not seem to work at all.

I would be grateful for any hints!