Should node finding use Newton or Gauss-Newton?

[inducer]

Upsides of Gauss-Newton:

• More robust?
• Gives us "the closest" if the exact point can't be found

Downside:

• Conditioning penalty via the normal equations

meshmode/meshmode/discretization/connection/opposite_face.py

Lines 136 to 153 in dd24703

	def _find_src_unit_nodes_via_gauss_newton(
	tgt_bdry_nodes,
	src_bdry_nodes,
	src_grp, src_mesh_grp,
	tgt_bdry_discr, src_bdry_discr,
	tol):
	dim = src_grp.dim
	_, nelements, ntgt_unit_nodes = tgt_bdry_nodes.shape
	initial_guess = np.mean(src_mesh_grp.vertex_unit_coordinates(), axis=0)
	src_unit_nodes = np.empty((dim, nelements, ntgt_unit_nodes))
	src_unit_nodes[:] = initial_guess.reshape(-1, 1, 1)
	import modepy as mp
	src_grp_basis_fcts = src_grp.basis_obj().functions
	vdm = mp.vandermonde(src_grp_basis_fcts, src_grp.unit_nodes)
	inv_t_vdm = la.inv(vdm.T)
	nsrc_funcs = len(src_grp_basis_fcts)

cc @xywei @alexfikl @majosm