LAPACK 3.3.1 Linear Algebra PACKage

# zgebak.f

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```00001       SUBROUTINE ZGEBAK( JOB, SIDE, N, ILO, IHI, SCALE, M, V, LDV,
00002      \$                   INFO )
00003 *
00004 *  -- LAPACK routine (version 3.2) --
00005 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00006 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00007 *     November 2006
00008 *
00009 *     .. Scalar Arguments ..
00010       CHARACTER          JOB, SIDE
00011       INTEGER            IHI, ILO, INFO, LDV, M, N
00012 *     ..
00013 *     .. Array Arguments ..
00014       DOUBLE PRECISION   SCALE( * )
00015       COMPLEX*16         V( LDV, * )
00016 *     ..
00017 *
00018 *  Purpose
00019 *  =======
00020 *
00021 *  ZGEBAK forms the right or left eigenvectors of a complex general
00022 *  matrix by backward transformation on the computed eigenvectors of the
00023 *  balanced matrix output by ZGEBAL.
00024 *
00025 *  Arguments
00026 *  =========
00027 *
00028 *  JOB     (input) CHARACTER*1
00029 *          Specifies the type of backward transformation required:
00030 *          = 'N', do nothing, return immediately;
00031 *          = 'P', do backward transformation for permutation only;
00032 *          = 'S', do backward transformation for scaling only;
00033 *          = 'B', do backward transformations for both permutation and
00034 *                 scaling.
00035 *          JOB must be the same as the argument JOB supplied to ZGEBAL.
00036 *
00037 *  SIDE    (input) CHARACTER*1
00038 *          = 'R':  V contains right eigenvectors;
00039 *          = 'L':  V contains left eigenvectors.
00040 *
00041 *  N       (input) INTEGER
00042 *          The number of rows of the matrix V.  N >= 0.
00043 *
00044 *  ILO     (input) INTEGER
00045 *  IHI     (input) INTEGER
00046 *          The integers ILO and IHI determined by ZGEBAL.
00047 *          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
00048 *
00049 *  SCALE   (input) DOUBLE PRECISION array, dimension (N)
00050 *          Details of the permutation and scaling factors, as returned
00051 *          by ZGEBAL.
00052 *
00053 *  M       (input) INTEGER
00054 *          The number of columns of the matrix V.  M >= 0.
00055 *
00056 *  V       (input/output) COMPLEX*16 array, dimension (LDV,M)
00057 *          On entry, the matrix of right or left eigenvectors to be
00058 *          transformed, as returned by ZHSEIN or ZTREVC.
00059 *          On exit, V is overwritten by the transformed eigenvectors.
00060 *
00061 *  LDV     (input) INTEGER
00062 *          The leading dimension of the array V. LDV >= max(1,N).
00063 *
00064 *  INFO    (output) INTEGER
00065 *          = 0:  successful exit
00066 *          < 0:  if INFO = -i, the i-th argument had an illegal value.
00067 *
00068 *  =====================================================================
00069 *
00070 *     .. Parameters ..
00071       DOUBLE PRECISION   ONE
00072       PARAMETER          ( ONE = 1.0D+0 )
00073 *     ..
00074 *     .. Local Scalars ..
00075       LOGICAL            LEFTV, RIGHTV
00076       INTEGER            I, II, K
00077       DOUBLE PRECISION   S
00078 *     ..
00079 *     .. External Functions ..
00080       LOGICAL            LSAME
00081       EXTERNAL           LSAME
00082 *     ..
00083 *     .. External Subroutines ..
00084       EXTERNAL           XERBLA, ZDSCAL, ZSWAP
00085 *     ..
00086 *     .. Intrinsic Functions ..
00087       INTRINSIC          MAX, MIN
00088 *     ..
00089 *     .. Executable Statements ..
00090 *
00091 *     Decode and Test the input parameters
00092 *
00093       RIGHTV = LSAME( SIDE, 'R' )
00094       LEFTV = LSAME( SIDE, 'L' )
00095 *
00096       INFO = 0
00097       IF( .NOT.LSAME( JOB, 'N' ) .AND. .NOT.LSAME( JOB, 'P' ) .AND.
00098      \$    .NOT.LSAME( JOB, 'S' ) .AND. .NOT.LSAME( JOB, 'B' ) ) THEN
00099          INFO = -1
00100       ELSE IF( .NOT.RIGHTV .AND. .NOT.LEFTV ) THEN
00101          INFO = -2
00102       ELSE IF( N.LT.0 ) THEN
00103          INFO = -3
00104       ELSE IF( ILO.LT.1 .OR. ILO.GT.MAX( 1, N ) ) THEN
00105          INFO = -4
00106       ELSE IF( IHI.LT.MIN( ILO, N ) .OR. IHI.GT.N ) THEN
00107          INFO = -5
00108       ELSE IF( M.LT.0 ) THEN
00109          INFO = -7
00110       ELSE IF( LDV.LT.MAX( 1, N ) ) THEN
00111          INFO = -9
00112       END IF
00113       IF( INFO.NE.0 ) THEN
00114          CALL XERBLA( 'ZGEBAK', -INFO )
00115          RETURN
00116       END IF
00117 *
00118 *     Quick return if possible
00119 *
00120       IF( N.EQ.0 )
00121      \$   RETURN
00122       IF( M.EQ.0 )
00123      \$   RETURN
00124       IF( LSAME( JOB, 'N' ) )
00125      \$   RETURN
00126 *
00127       IF( ILO.EQ.IHI )
00128      \$   GO TO 30
00129 *
00130 *     Backward balance
00131 *
00132       IF( LSAME( JOB, 'S' ) .OR. LSAME( JOB, 'B' ) ) THEN
00133 *
00134          IF( RIGHTV ) THEN
00135             DO 10 I = ILO, IHI
00136                S = SCALE( I )
00137                CALL ZDSCAL( M, S, V( I, 1 ), LDV )
00138    10       CONTINUE
00139          END IF
00140 *
00141          IF( LEFTV ) THEN
00142             DO 20 I = ILO, IHI
00143                S = ONE / SCALE( I )
00144                CALL ZDSCAL( M, S, V( I, 1 ), LDV )
00145    20       CONTINUE
00146          END IF
00147 *
00148       END IF
00149 *
00150 *     Backward permutation
00151 *
00152 *     For  I = ILO-1 step -1 until 1,
00153 *              IHI+1 step 1 until N do --
00154 *
00155    30 CONTINUE
00156       IF( LSAME( JOB, 'P' ) .OR. LSAME( JOB, 'B' ) ) THEN
00157          IF( RIGHTV ) THEN
00158             DO 40 II = 1, N
00159                I = II
00160                IF( I.GE.ILO .AND. I.LE.IHI )
00161      \$            GO TO 40
00162                IF( I.LT.ILO )
00163      \$            I = ILO - II
00164                K = SCALE( I )
00165                IF( K.EQ.I )
00166      \$            GO TO 40
00167                CALL ZSWAP( M, V( I, 1 ), LDV, V( K, 1 ), LDV )
00168    40       CONTINUE
00169          END IF
00170 *
00171          IF( LEFTV ) THEN
00172             DO 50 II = 1, N
00173                I = II
00174                IF( I.GE.ILO .AND. I.LE.IHI )
00175      \$            GO TO 50
00176                IF( I.LT.ILO )
00177      \$            I = ILO - II
00178                K = SCALE( I )
00179                IF( K.EQ.I )
00180      \$            GO TO 50
00181                CALL ZSWAP( M, V( I, 1 ), LDV, V( K, 1 ), LDV )
00182    50       CONTINUE
00183          END IF
00184       END IF
00185 *
00186       RETURN
00187 *
00188 *     End of ZGEBAK
00189 *
00190       END
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