1549301742-The_Theory_of_Difference_Schemes__Samarskii

(jair2018) #1
The alternative-triangular inethod 685

with
0 8
li = -------
l+w8+±w28~'

0 1
(28) l? -=-, 2w

where an operator B is specified by formula (22). The ratio

0
~

attains its n1aximal value for

(29) W = w 0 =

2
18/S.,

giving in that case

0 2 y'1)
~=l+fo'

0 8
(30) l 1 = 2 ( 1 + y'i)) ,

Proof Inequalities (25) and (26) together irnply that


(Ry,y) > 8(y,y),


whence it follows that 8 < ~ and 17 < 1.
Before giving further inotivations, we may atte1npt operator (22) in
the fonn

With the relations R > 8E or E < t R in view, we obtain for the operator
B the upper estimate

B<-R+wR+--R=^1 w^2 ~ (l -+w+--w^2 ~) R=-R^1
-5 4 8 4 ~. ,
I I
0
yielding the relation R > / 1 B. Formula (31) transforms into


= (E - w Ri) (E - w R2) + 2w R,

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