I'm familiar with finding the order of accuracy using von Neumann analysis for finite difference schemes formulated using Taylor series expansions.But is there a similar technique for finding the order of accuracy for schemes that use a least squares fit for approximating gradients?Currently, I am solving a 1D advection equation in advective form.  I'm using Forward Euler timestepping and an upwind quadratic least squares fit with a three-point stencil.  My experiments suggest an order of accuracy of ~0.7 which suggests that I've either got bugs in my implementation or the scheme is inherently slow to converge.
Calculating theoretical order of accuracy of least squares fit advection scheme
finite difference;numerical analysis;least squares;advection