Hello users and developers,

I am simulating a simple parabolic poiseuille flow case, and trying to compute shear rates. I input my geometry as an STL file. I get the expected velocity field. However, when I compute the shear rate, I get weird values of shear rate in the envelope regions. I have attached a visualization here. Any suggestions how to avoid this? At the exact boundary of my domain, it would help to use a forward or backward finite difference scheme as opposed to the centered finite differences used by computeStrainRate

Here is my writeVTK function:

```
void writeVTK(MultiBlockLattice3D<T,DESCRIPTOR>& lattice,
T dx, T dt, plint iter)
{
auto vel = *computeVelocity(lattice);
ParallelVtkImageOutput3D<T> vtkOut(createFileName("vtk", iter, 6), 3, dx);
vtkOut.writeData<T>(*computeVelocityNorm(lattice), "velocityNorm", dx/dt);
vtkOut.writeData<3,T>(vel, "velocity", dx/dt);
vtkOut.writeData<T>(*computeSymmetricTensorNorm(*computeStrainRate(vel, lattice.getBoundingBox()), lattice.getBoundingBox()), "shear", 1/dt);
}
```