Some devices are not fast enough to differentiate between a fast-moving
contact and a new contact. This problem cannot be fully resolved because
information is truly missing, but it is possible to safe-guard against
obvious mistakes by restricting movement with a maximum displacement.

The new problem formulation for dmax > 0 cannot benefit from the speedup
for positive definite matrices, but since the convergence is faster, the
result is about the same. For a handful of contacts, the latency difference
is truly negligible.
Suggested-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: NHenrik Rydberg <rydberg@bitmath.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>