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.