The optimal delay range for LIF is known to be around
half of the order, in this interval the worst case being
for odd order
N and 
for even N. Furthermore,
as experimentally noticed in [Laakso et al., 1996], the LIFs are passive
filters (i.e. their gain is less than 1) when the delay verifies
relation (7). This condition is necessary for
applications which involve feedback loops since a non-passive
component in a feedback loop may cause numerical instabilities.
Finally for each value of delay, two different LIFs, resp. order
and order 
, verify relation (7).
