SCALAPACK 2.2.2
LAPACK: Linear Algebra PACKage
Loading...
Searching...
No Matches

◆ dlasorte()

subroutine dlasorte ( double precision, dimension( lds, * )  s,
integer  lds,
integer  j,
double precision, dimension( j, * )  out,
integer  info 
)

Definition at line 1 of file dlasorte.f.

2*
3* -- ScaLAPACK routine (version 1.7) --
4* University of Tennessee, Knoxville, Oak Ridge National Laboratory,
5* and University of California, Berkeley.
6* December 31, 1998
7*
8* .. Scalar Arguments ..
9 INTEGER INFO, J, LDS
10* ..
11* .. Array Arguments ..
12 DOUBLE PRECISION OUT( J, * ), S( LDS, * )
13* ..
14*
15* Purpose
16* =======
17*
18* DLASORTE sorts eigenpairs so that real eigenpairs are together and
19* complex are together. This way one can employ 2x2 shifts easily
20* since every 2nd subdiagonal is guaranteed to be zero.
21* This routine does no parallel work.
22*
23* Arguments
24* =========
25*
26* S (local input/output) DOUBLE PRECISION array, dimension LDS
27* On entry, a matrix already in Schur form.
28* On exit, the diagonal blocks of S have been rewritten to pair
29* the eigenvalues. The resulting matrix is no longer
30* similar to the input.
31*
32* LDS (local input) INTEGER
33* On entry, the leading dimension of the local array S.
34* Unchanged on exit.
35*
36* J (local input) INTEGER
37* On entry, the order of the matrix S.
38* Unchanged on exit.
39*
40* OUT (local input/output) DOUBLE PRECISION array, dimension Jx2
41* This is the work buffer required by this routine.
42*
43* INFO (local input) INTEGER
44* This is set if the input matrix had an odd number of real
45* eigenvalues and things couldn't be paired or if the input
46* matrix S was not originally in Schur form.
47* 0 indicates successful completion.
48*
49* Implemented by: G. Henry, November 17, 1996
50*
51* =====================================================================
52*
53* .. Parameters ..
54 DOUBLE PRECISION ZERO
55 parameter( zero = 0.0d+0 )
56* ..
57* .. Local Scalars ..
58 INTEGER BOT, I, LAST, TOP
59* ..
60* .. Intrinsic Functions ..
61 INTRINSIC mod
62* ..
63* .. Executable Statements ..
64*
65 last = j
66 top = 1
67 bot = j
68 info = 0
69 DO 10 i = j - 1, 1, -1
70 IF( s( i+1, i ).EQ.zero ) THEN
71 IF( last-i.EQ.2 ) THEN
72 out( bot-1, 1 ) = s( i+1, i+1 )
73 out( bot, 2 ) = s( i+2, i+2 )
74 out( bot-1, 2 ) = s( i+1, i+2 )
75 out( bot, 1 ) = s( i+2, i+1 )
76 bot = bot - 2
77 END IF
78 IF( last-i.EQ.1 ) THEN
79 IF( mod( top, 2 ).EQ.1 ) THEN
80*
81* FIRST OF A PAIR
82*
83 IF( ( i.EQ.j-1 ) .OR. ( i.EQ.1 ) ) THEN
84 out( top, 1 ) = s( i+1, i+1 )
85 ELSE
86 out( top, 1 ) = s( i+1, i+1 )
87 END IF
88 out( top, 2 ) = zero
89 ELSE
90*
91* SECOND OF A PAIR
92*
93 IF( ( i.EQ.j-1 ) .OR. ( i.EQ.1 ) ) THEN
94 out( top, 2 ) = s( i+1, i+1 )
95 ELSE
96 out( top, 2 ) = s( i+1, i+1 )
97 END IF
98 out( top, 1 ) = zero
99 END IF
100 top = top + 1
101 END IF
102 IF( last-i.GT.2 ) THEN
103 info = i
104 RETURN
105 END IF
106 last = i
107 END IF
108 10 CONTINUE
109 IF( last.EQ.2 ) THEN
110*
111* GRAB LAST DOUBLE PAIR
112*
113 out( bot-1, 1 ) = s( 1, 1 )
114 out( bot, 2 ) = s( 2, 2 )
115 out( bot-1, 2 ) = s( 1, 2 )
116 out( bot, 1 ) = s( 2, 1 )
117 bot = bot - 2
118 END IF
119 IF( last.EQ.1 .and. mod(top, 2) .eq. 0 ) THEN
120*
121* GRAB SECOND PART OF LAST PAIR
122*
123 out(top, 2) = s(1,1)
124 out(top, 1) = zero
125 top = top + 1
126 END IF
127 IF( top-1.NE.bot ) THEN
128 info = -bot
129 RETURN
130 END IF
131*
132* Overwrite the S diagonals
133*
134 DO 20 i = 1, j, 2
135 s( i, i ) = out( i, 1 )
136 s( i+1, i ) = out( i+1, 1 )
137 s( i, i+1 ) = out( i, 2 )
138 s( i+1, i+1 ) = out( i+1, 2 )
139 20 CONTINUE
140*
141 RETURN
142*
143* End of DLASORTE
144*
Here is the caller graph for this function: