d9/d49/schkbk_8f_source.html

00001       SUBROUTINE SCHKBK( NIN, NOUT )
00002 *
00003 *  -- LAPACK test routine (version 3.1) --
00004 *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
00005 *     November 2006
00006 *
00007 *     .. Scalar Arguments ..
00008       INTEGER            NIN, NOUT
00009 *     ..
00010 *
00011 *  Purpose
00012 *  =======
00013 *
00014 *  SCHKBK tests SGEBAK, a routine for backward transformation of
00015 *  the computed right or left eigenvectors if the orginal matrix
00016 *  was preprocessed by balance subroutine SGEBAL.
00017 *
00018 *  Arguments
00019 *  =========
00020 *
00021 *  NIN     (input) INTEGER
00022 *          The logical unit number for input.  NIN > 0.
00023 *
00024 *  NOUT    (input) INTEGER
00025 *          The logical unit number for output.  NOUT > 0.
00026 *
00027 * ======================================================================
00028 *
00029 *     .. Parameters ..
00030       INTEGER            LDE
00031       PARAMETER          ( LDE = 20 )
00032       REAL               ZERO
00033       PARAMETER          ( ZERO = 0.0E0 )
00034 *     ..
00035 *     .. Local Scalars ..
00036       INTEGER            I, IHI, ILO, INFO, J, KNT, N, NINFO
00037       REAL               EPS, RMAX, SAFMIN, VMAX, X
00038 *     ..
00039 *     .. Local Arrays ..
00040       INTEGER            LMAX( 2 )
00041       REAL               E( LDE, LDE ), EIN( LDE, LDE ), SCALE( LDE )
00042 *     ..
00043 *     .. External Functions ..
00044       REAL               SLAMCH
00045       EXTERNAL           SLAMCH
00046 *     ..
00047 *     .. External Subroutines ..
00048       EXTERNAL           SGEBAK
00049 *     ..
00050 *     .. Intrinsic Functions ..
00051       INTRINSIC          ABS, MAX
00052 *     ..
00053 *     .. Executable Statements ..
00054 *
00055       LMAX( 1 ) = 0
00056       LMAX( 2 ) = 0
00057       NINFO = 0
00058       KNT = 0
00059       RMAX = ZERO
00060       EPS = SLAMCH( 'E' )
00061       SAFMIN = SLAMCH( 'S' )
00062 *
00063    10 CONTINUE
00064 *
00065       READ( NIN, FMT = * )N, ILO, IHI
00066       IF( N.EQ.0 )
00067      $   GO TO 60
00068 *
00069       READ( NIN, FMT = * )( SCALE( I ), I = 1, N )
00070       DO 20 I = 1, N
00071          READ( NIN, FMT = * )( E( I, J ), J = 1, N )
00072    20 CONTINUE
00073 *
00074       DO 30 I = 1, N
00075          READ( NIN, FMT = * )( EIN( I, J ), J = 1, N )
00076    30 CONTINUE
00077 *
00078       KNT = KNT + 1
00079       CALL SGEBAK( 'B', 'R', N, ILO, IHI, SCALE, N, E, LDE, INFO )
00080 *
00081       IF( INFO.NE.0 ) THEN
00082          NINFO = NINFO + 1
00083          LMAX( 1 ) = KNT
00084       END IF
00085 *
00086       VMAX = ZERO
00087       DO 50 I = 1, N
00088          DO 40 J = 1, N
00089             X = ABS( E( I, J )-EIN( I, J ) ) / EPS
00090             IF( ABS( E( I, J ) ).GT.SAFMIN )
00091      $         X = X / ABS( E( I, J ) )
00092             VMAX = MAX( VMAX, X )
00093    40    CONTINUE
00094    50 CONTINUE
00095 *
00096       IF( VMAX.GT.RMAX ) THEN
00097          LMAX( 2 ) = KNT
00098          RMAX = VMAX
00099       END IF
00100 *
00101       GO TO 10
00102 *
00103    60 CONTINUE
00104 *
00105       WRITE( NOUT, FMT = 9999 )
00106  9999 FORMAT( 1X, '.. test output of SGEBAK .. ' )
00107 *
00108       WRITE( NOUT, FMT = 9998 )RMAX
00109  9998 FORMAT( 1X, 'value of largest test error             = ', E12.3 )
00110       WRITE( NOUT, FMT = 9997 )LMAX( 1 )
00111  9997 FORMAT( 1X, 'example number where info is not zero   = ', I4 )
00112       WRITE( NOUT, FMT = 9996 )LMAX( 2 )
00113  9996 FORMAT( 1X, 'example number having largest error     = ', I4 )
00114       WRITE( NOUT, FMT = 9995 )NINFO
00115  9995 FORMAT( 1X, 'number of examples where info is not 0  = ', I4 )
00116       WRITE( NOUT, FMT = 9994 )KNT
00117  9994 FORMAT( 1X, 'total number of examples tested         = ', I4 )
00118 *
00119       RETURN
00120 *
00121 *     End of SCHKBK
00122 *
00123       END