The alternating direction niethod 557
with further reference to the following asymptotic relations:
As a final result we obtain
thereby justifying that scheme (33)-(34) generates a second-order approx-
i1nation:
Further developn1ent of s01ne a priori estin1ate for a solution of the
problem concerned is mostly based on an operator-difference analog of prob-
lem (37)-(38) such as
(39)
zn+l - z
0.5 T + A l ( in+l/2 ) Z -+ A 2 ( in+l ) Z n+l =^0 'f/2 /,'11 '
n=0,1,2,. .. , z(O)=O,
where A 1 (t) and A 2 (t) are linear operators in a Hilbert space H:
At : H c--H,