LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
dtbcon.f
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00001 *> \brief \b DTBCON
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download DTBCON + dependencies 
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00011 *> [TGZ]</a> 
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00013 *> [ZIP]</a> 
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00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       SUBROUTINE DTBCON( NORM, UPLO, DIAG, N, KD, AB, LDAB, RCOND, WORK,
00022 *                          IWORK, INFO )
00023 * 
00024 *       .. Scalar Arguments ..
00025 *       CHARACTER          DIAG, NORM, UPLO
00026 *       INTEGER            INFO, KD, LDAB, N
00027 *       DOUBLE PRECISION   RCOND
00028 *       ..
00029 *       .. Array Arguments ..
00030 *       INTEGER            IWORK( * )
00031 *       DOUBLE PRECISION   AB( LDAB, * ), WORK( * )
00032 *       ..
00033 *  
00034 *
00035 *> \par Purpose:
00036 *  =============
00037 *>
00038 *> \verbatim
00039 *>
00040 *> DTBCON estimates the reciprocal of the condition number of a
00041 *> triangular band matrix A, in either the 1-norm or the infinity-norm.
00042 *>
00043 *> The norm of A is computed and an estimate is obtained for
00044 *> norm(inv(A)), then the reciprocal of the condition number is
00045 *> computed as
00046 *>    RCOND = 1 / ( norm(A) * norm(inv(A)) ).
00047 *> \endverbatim
00048 *
00049 *  Arguments:
00050 *  ==========
00051 *
00052 *> \param[in] NORM
00053 *> \verbatim
00054 *>          NORM is CHARACTER*1
00055 *>          Specifies whether the 1-norm condition number or the
00056 *>          infinity-norm condition number is required:
00057 *>          = '1' or 'O':  1-norm;
00058 *>          = 'I':         Infinity-norm.
00059 *> \endverbatim
00060 *>
00061 *> \param[in] UPLO
00062 *> \verbatim
00063 *>          UPLO is CHARACTER*1
00064 *>          = 'U':  A is upper triangular;
00065 *>          = 'L':  A is lower triangular.
00066 *> \endverbatim
00067 *>
00068 *> \param[in] DIAG
00069 *> \verbatim
00070 *>          DIAG is CHARACTER*1
00071 *>          = 'N':  A is non-unit triangular;
00072 *>          = 'U':  A is unit triangular.
00073 *> \endverbatim
00074 *>
00075 *> \param[in] N
00076 *> \verbatim
00077 *>          N is INTEGER
00078 *>          The order of the matrix A.  N >= 0.
00079 *> \endverbatim
00080 *>
00081 *> \param[in] KD
00082 *> \verbatim
00083 *>          KD is INTEGER
00084 *>          The number of superdiagonals or subdiagonals of the
00085 *>          triangular band matrix A.  KD >= 0.
00086 *> \endverbatim
00087 *>
00088 *> \param[in] AB
00089 *> \verbatim
00090 *>          AB is DOUBLE PRECISION array, dimension (LDAB,N)
00091 *>          The upper or lower triangular band matrix A, stored in the
00092 *>          first kd+1 rows of the array. The j-th column of A is stored
00093 *>          in the j-th column of the array AB as follows:
00094 *>          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
00095 *>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).
00096 *>          If DIAG = 'U', the diagonal elements of A are not referenced
00097 *>          and are assumed to be 1.
00098 *> \endverbatim
00099 *>
00100 *> \param[in] LDAB
00101 *> \verbatim
00102 *>          LDAB is INTEGER
00103 *>          The leading dimension of the array AB.  LDAB >= KD+1.
00104 *> \endverbatim
00105 *>
00106 *> \param[out] RCOND
00107 *> \verbatim
00108 *>          RCOND is DOUBLE PRECISION
00109 *>          The reciprocal of the condition number of the matrix A,
00110 *>          computed as RCOND = 1/(norm(A) * norm(inv(A))).
00111 *> \endverbatim
00112 *>
00113 *> \param[out] WORK
00114 *> \verbatim
00115 *>          WORK is DOUBLE PRECISION array, dimension (3*N)
00116 *> \endverbatim
00117 *>
00118 *> \param[out] IWORK
00119 *> \verbatim
00120 *>          IWORK is INTEGER array, dimension (N)
00121 *> \endverbatim
00122 *>
00123 *> \param[out] INFO
00124 *> \verbatim
00125 *>          INFO is INTEGER
00126 *>          = 0:  successful exit
00127 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
00128 *> \endverbatim
00129 *
00130 *  Authors:
00131 *  ========
00132 *
00133 *> \author Univ. of Tennessee 
00134 *> \author Univ. of California Berkeley 
00135 *> \author Univ. of Colorado Denver 
00136 *> \author NAG Ltd. 
00137 *
00138 *> \date November 2011
00139 *
00140 *> \ingroup doubleOTHERcomputational
00141 *
00142 *  =====================================================================
00143       SUBROUTINE DTBCON( NORM, UPLO, DIAG, N, KD, AB, LDAB, RCOND, WORK,
00144      $                   IWORK, INFO )
00145 *
00146 *  -- LAPACK computational routine (version 3.4.0) --
00147 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00148 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00149 *     November 2011
00150 *
00151 *     .. Scalar Arguments ..
00152       CHARACTER          DIAG, NORM, UPLO
00153       INTEGER            INFO, KD, LDAB, N
00154       DOUBLE PRECISION   RCOND
00155 *     ..
00156 *     .. Array Arguments ..
00157       INTEGER            IWORK( * )
00158       DOUBLE PRECISION   AB( LDAB, * ), WORK( * )
00159 *     ..
00160 *
00161 *  =====================================================================
00162 *
00163 *     .. Parameters ..
00164       DOUBLE PRECISION   ONE, ZERO
00165       PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
00166 *     ..
00167 *     .. Local Scalars ..
00168       LOGICAL            NOUNIT, ONENRM, UPPER
00169       CHARACTER          NORMIN
00170       INTEGER            IX, KASE, KASE1
00171       DOUBLE PRECISION   AINVNM, ANORM, SCALE, SMLNUM, XNORM
00172 *     ..
00173 *     .. Local Arrays ..
00174       INTEGER            ISAVE( 3 )
00175 *     ..
00176 *     .. External Functions ..
00177       LOGICAL            LSAME
00178       INTEGER            IDAMAX
00179       DOUBLE PRECISION   DLAMCH, DLANTB
00180       EXTERNAL           LSAME, IDAMAX, DLAMCH, DLANTB
00181 *     ..
00182 *     .. External Subroutines ..
00183       EXTERNAL           DLACN2, DLATBS, DRSCL, XERBLA
00184 *     ..
00185 *     .. Intrinsic Functions ..
00186       INTRINSIC          ABS, DBLE, MAX
00187 *     ..
00188 *     .. Executable Statements ..
00189 *
00190 *     Test the input parameters.
00191 *
00192       INFO = 0
00193       UPPER = LSAME( UPLO, 'U' )
00194       ONENRM = NORM.EQ.'1' .OR. LSAME( NORM, 'O' )
00195       NOUNIT = LSAME( DIAG, 'N' )
00196 *
00197       IF( .NOT.ONENRM .AND. .NOT.LSAME( NORM, 'I' ) ) THEN
00198          INFO = -1
00199       ELSE IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
00200          INFO = -2
00201       ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
00202          INFO = -3
00203       ELSE IF( N.LT.0 ) THEN
00204          INFO = -4
00205       ELSE IF( KD.LT.0 ) THEN
00206          INFO = -5
00207       ELSE IF( LDAB.LT.KD+1 ) THEN
00208          INFO = -7
00209       END IF
00210       IF( INFO.NE.0 ) THEN
00211          CALL XERBLA( 'DTBCON', -INFO )
00212          RETURN
00213       END IF
00214 *
00215 *     Quick return if possible
00216 *
00217       IF( N.EQ.0 ) THEN
00218          RCOND = ONE
00219          RETURN
00220       END IF
00221 *
00222       RCOND = ZERO
00223       SMLNUM = DLAMCH( 'Safe minimum' )*DBLE( MAX( 1, N ) )
00224 *
00225 *     Compute the norm of the triangular matrix A.
00226 *
00227       ANORM = DLANTB( NORM, UPLO, DIAG, N, KD, AB, LDAB, WORK )
00228 *
00229 *     Continue only if ANORM > 0.
00230 *
00231       IF( ANORM.GT.ZERO ) THEN
00232 *
00233 *        Estimate the norm of the inverse of A.
00234 *
00235          AINVNM = ZERO
00236          NORMIN = 'N'
00237          IF( ONENRM ) THEN
00238             KASE1 = 1
00239          ELSE
00240             KASE1 = 2
00241          END IF
00242          KASE = 0
00243    10    CONTINUE
00244          CALL DLACN2( N, WORK( N+1 ), WORK, IWORK, AINVNM, KASE, ISAVE )
00245          IF( KASE.NE.0 ) THEN
00246             IF( KASE.EQ.KASE1 ) THEN
00247 *
00248 *              Multiply by inv(A).
00249 *
00250                CALL DLATBS( UPLO, 'No transpose', DIAG, NORMIN, N, KD,
00251      $                      AB, LDAB, WORK, SCALE, WORK( 2*N+1 ), INFO )
00252             ELSE
00253 *
00254 *              Multiply by inv(A**T).
00255 *
00256                CALL DLATBS( UPLO, 'Transpose', DIAG, NORMIN, N, KD, AB,
00257      $                      LDAB, WORK, SCALE, WORK( 2*N+1 ), INFO )
00258             END IF
00259             NORMIN = 'Y'
00260 *
00261 *           Multiply by 1/SCALE if doing so will not cause overflow.
00262 *
00263             IF( SCALE.NE.ONE ) THEN
00264                IX = IDAMAX( N, WORK, 1 )
00265                XNORM = ABS( WORK( IX ) )
00266                IF( SCALE.LT.XNORM*SMLNUM .OR. SCALE.EQ.ZERO )
00267      $            GO TO 20
00268                CALL DRSCL( N, SCALE, WORK, 1 )
00269             END IF
00270             GO TO 10
00271          END IF
00272 *
00273 *        Compute the estimate of the reciprocal condition number.
00274 *
00275          IF( AINVNM.NE.ZERO )
00276      $      RCOND = ( ONE / ANORM ) / AINVNM
00277       END IF
00278 *
00279    20 CONTINUE
00280       RETURN
00281 *
00282 *     End of DTBCON
00283 *
00284       END
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