LAPACK 3.3.1 Linear Algebra PACKage

# cgecon.f

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```00001       SUBROUTINE CGECON( NORM, N, A, LDA, ANORM, RCOND, WORK, RWORK,
00002      \$                   INFO )
00003 *
00004 *  -- LAPACK routine (version 3.3.1) --
00005 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00006 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00007 *  -- April 2011                                                      --
00008 *
00009 *     Modified to call CLACN2 in place of CLACON, 10 Feb 03, SJH.
00010 *
00011 *     .. Scalar Arguments ..
00012       CHARACTER          NORM
00013       INTEGER            INFO, LDA, N
00014       REAL               ANORM, RCOND
00015 *     ..
00016 *     .. Array Arguments ..
00017       REAL               RWORK( * )
00018       COMPLEX            A( LDA, * ), WORK( * )
00019 *     ..
00020 *
00021 *  Purpose
00022 *  =======
00023 *
00024 *  CGECON estimates the reciprocal of the condition number of a general
00025 *  complex matrix A, in either the 1-norm or the infinity-norm, using
00026 *  the LU factorization computed by CGETRF.
00027 *
00028 *  An estimate is obtained for norm(inv(A)), and the reciprocal of the
00029 *  condition number is computed as
00030 *     RCOND = 1 / ( norm(A) * norm(inv(A)) ).
00031 *
00032 *  Arguments
00033 *  =========
00034 *
00035 *  NORM    (input) CHARACTER*1
00036 *          Specifies whether the 1-norm condition number or the
00037 *          infinity-norm condition number is required:
00038 *          = '1' or 'O':  1-norm;
00039 *          = 'I':         Infinity-norm.
00040 *
00041 *  N       (input) INTEGER
00042 *          The order of the matrix A.  N >= 0.
00043 *
00044 *  A       (input) COMPLEX array, dimension (LDA,N)
00045 *          The factors L and U from the factorization A = P*L*U
00046 *          as computed by CGETRF.
00047 *
00048 *  LDA     (input) INTEGER
00049 *          The leading dimension of the array A.  LDA >= max(1,N).
00050 *
00051 *  ANORM   (input) REAL
00052 *          If NORM = '1' or 'O', the 1-norm of the original matrix A.
00053 *          If NORM = 'I', the infinity-norm of the original matrix A.
00054 *
00055 *  RCOND   (output) REAL
00056 *          The reciprocal of the condition number of the matrix A,
00057 *          computed as RCOND = 1/(norm(A) * norm(inv(A))).
00058 *
00059 *  WORK    (workspace) COMPLEX array, dimension (2*N)
00060 *
00061 *  RWORK   (workspace) REAL array, dimension (2*N)
00062 *
00063 *  INFO    (output) INTEGER
00064 *          = 0:  successful exit
00065 *          < 0:  if INFO = -i, the i-th argument had an illegal value
00066 *
00067 *  =====================================================================
00068 *
00069 *     .. Parameters ..
00070       REAL               ONE, ZERO
00071       PARAMETER          ( ONE = 1.0E+0, ZERO = 0.0E+0 )
00072 *     ..
00073 *     .. Local Scalars ..
00074       LOGICAL            ONENRM
00075       CHARACTER          NORMIN
00076       INTEGER            IX, KASE, KASE1
00077       REAL               AINVNM, SCALE, SL, SMLNUM, SU
00078       COMPLEX            ZDUM
00079 *     ..
00080 *     .. Local Arrays ..
00081       INTEGER            ISAVE( 3 )
00082 *     ..
00083 *     .. External Functions ..
00084       LOGICAL            LSAME
00085       INTEGER            ICAMAX
00086       REAL               SLAMCH
00087       EXTERNAL           LSAME, ICAMAX, SLAMCH
00088 *     ..
00089 *     .. External Subroutines ..
00090       EXTERNAL           CLACN2, CLATRS, CSRSCL, XERBLA
00091 *     ..
00092 *     .. Intrinsic Functions ..
00093       INTRINSIC          ABS, AIMAG, MAX, REAL
00094 *     ..
00095 *     .. Statement Functions ..
00096       REAL               CABS1
00097 *     ..
00098 *     .. Statement Function definitions ..
00099       CABS1( ZDUM ) = ABS( REAL( ZDUM ) ) + ABS( AIMAG( ZDUM ) )
00100 *     ..
00101 *     .. Executable Statements ..
00102 *
00103 *     Test the input parameters.
00104 *
00105       INFO = 0
00106       ONENRM = NORM.EQ.'1' .OR. LSAME( NORM, 'O' )
00107       IF( .NOT.ONENRM .AND. .NOT.LSAME( NORM, 'I' ) ) THEN
00108          INFO = -1
00109       ELSE IF( N.LT.0 ) THEN
00110          INFO = -2
00111       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
00112          INFO = -4
00113       ELSE IF( ANORM.LT.ZERO ) THEN
00114          INFO = -5
00115       END IF
00116       IF( INFO.NE.0 ) THEN
00117          CALL XERBLA( 'CGECON', -INFO )
00118          RETURN
00119       END IF
00120 *
00121 *     Quick return if possible
00122 *
00123       RCOND = ZERO
00124       IF( N.EQ.0 ) THEN
00125          RCOND = ONE
00126          RETURN
00127       ELSE IF( ANORM.EQ.ZERO ) THEN
00128          RETURN
00129       END IF
00130 *
00131       SMLNUM = SLAMCH( 'Safe minimum' )
00132 *
00133 *     Estimate the norm of inv(A).
00134 *
00135       AINVNM = ZERO
00136       NORMIN = 'N'
00137       IF( ONENRM ) THEN
00138          KASE1 = 1
00139       ELSE
00140          KASE1 = 2
00141       END IF
00142       KASE = 0
00143    10 CONTINUE
00144       CALL CLACN2( N, WORK( N+1 ), WORK, AINVNM, KASE, ISAVE )
00145       IF( KASE.NE.0 ) THEN
00146          IF( KASE.EQ.KASE1 ) THEN
00147 *
00148 *           Multiply by inv(L).
00149 *
00150             CALL CLATRS( 'Lower', 'No transpose', 'Unit', NORMIN, N, A,
00151      \$                   LDA, WORK, SL, RWORK, INFO )
00152 *
00153 *           Multiply by inv(U).
00154 *
00155             CALL CLATRS( 'Upper', 'No transpose', 'Non-unit', NORMIN, N,
00156      \$                   A, LDA, WORK, SU, RWORK( N+1 ), INFO )
00157          ELSE
00158 *
00159 *           Multiply by inv(U**H).
00160 *
00161             CALL CLATRS( 'Upper', 'Conjugate transpose', 'Non-unit',
00162      \$                   NORMIN, N, A, LDA, WORK, SU, RWORK( N+1 ),
00163      \$                   INFO )
00164 *
00165 *           Multiply by inv(L**H).
00166 *
00167             CALL CLATRS( 'Lower', 'Conjugate transpose', 'Unit', NORMIN,
00168      \$                   N, A, LDA, WORK, SL, RWORK, INFO )
00169          END IF
00170 *
00171 *        Divide X by 1/(SL*SU) if doing so will not cause overflow.
00172 *
00173          SCALE = SL*SU
00174          NORMIN = 'Y'
00175          IF( SCALE.NE.ONE ) THEN
00176             IX = ICAMAX( N, WORK, 1 )
00177             IF( SCALE.LT.CABS1( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO )
00178      \$         GO TO 20
00179             CALL CSRSCL( N, SCALE, WORK, 1 )
00180          END IF
00181          GO TO 10
00182       END IF
00183 *
00184 *     Compute the estimate of the reciprocal condition number.
00185 *
00186       IF( AINVNM.NE.ZERO )
00187      \$   RCOND = ( ONE / AINVNM ) / ANORM
00188 *
00189    20 CONTINUE
00190       RETURN
00191 *
00192 *     End of CGECON
00193 *
00194       END
```