The choice of starting point for the phase generation by direct methods is crucial since if one starts
with a triplet phase invariant which, for example, leads immediately to a poorly indicated phase with a
large error then these initial errors will tend to propagate through the phase determination process
and in general lead to a poor or incorrect solution. The convergence method is a means by which a
starting point for phase generation can be found which will, with more certainty, lead to well
determined phases from multiple indications in the early stages of the phasing procedure.
The strength of a phase relationship may be judged by the value of 
from
Eq. 
. However since there is no phase information available at these early stages
this cannot be used. Germain et al [36] showed that an expected value
of 
, 
may be calculated without prior phase information
by replacing the 
and 
terms of Eq. with their respective expectation
values [24]. Thus it is possible to calculate 
for each of the triplet
phase relationships found in step 2 above.
The convergence method is an iterative procedure by which the reflection with the minimum value
of 
is temporarily removed from the list of reflections along with all phase
relationships which indicate its phase. (N.B. structure semi-invariants are not removed from the reflection
list). A new list of 
's is calculated from the updated set of phase
relationships and the procedure is repeated. In this way the procedure converges towards a set of
reflections which will give strong indications for new phases in the early stages of phase
generation with the weighted Tangent formula.