```      SUBROUTINE DPOCON( UPLO, N, A, LDA, ANORM, RCOND, WORK, IWORK,
\$                   INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     Modified to call DLACN2 in place of DLACON, 5 Feb 03, SJH.
*
*     .. Scalar Arguments ..
CHARACTER          UPLO
INTEGER            INFO, LDA, N
DOUBLE PRECISION   ANORM, RCOND
*     ..
*     .. Array Arguments ..
INTEGER            IWORK( * )
DOUBLE PRECISION   A( LDA, * ), WORK( * )
*     ..
*
*  Purpose
*  =======
*
*  DPOCON estimates the reciprocal of the condition number (in the
*  1-norm) of a real symmetric positive definite matrix using the
*  Cholesky factorization A = U**T*U or A = L*L**T computed by DPOTRF.
*
*  An estimate is obtained for norm(inv(A)), and the reciprocal of the
*  condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
*
*  Arguments
*  =========
*
*  UPLO    (input) CHARACTER*1
*          = 'U':  Upper triangle of A is stored;
*          = 'L':  Lower triangle of A is stored.
*
*  N       (input) INTEGER
*          The order of the matrix A.  N >= 0.
*
*  A       (input) DOUBLE PRECISION array, dimension (LDA,N)
*          The triangular factor U or L from the Cholesky factorization
*          A = U**T*U or A = L*L**T, as computed by DPOTRF.
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A.  LDA >= max(1,N).
*
*  ANORM   (input) DOUBLE PRECISION
*          The 1-norm (or infinity-norm) of the symmetric matrix A.
*
*  RCOND   (output) DOUBLE PRECISION
*          The reciprocal of the condition number of the matrix A,
*          computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an
*          estimate of the 1-norm of inv(A) computed in this routine.
*
*  WORK    (workspace) DOUBLE PRECISION array, dimension (3*N)
*
*  IWORK   (workspace) INTEGER array, dimension (N)
*
*  INFO    (output) INTEGER
*          = 0:  successful exit
*          < 0:  if INFO = -i, the i-th argument had an illegal value
*
*  =====================================================================
*
*     .. Parameters ..
DOUBLE PRECISION   ONE, ZERO
PARAMETER          ( ONE = 1.0D+0, ZERO = 0.0D+0 )
*     ..
*     .. Local Scalars ..
LOGICAL            UPPER
CHARACTER          NORMIN
INTEGER            IX, KASE
DOUBLE PRECISION   AINVNM, SCALE, SCALEL, SCALEU, SMLNUM
*     ..
*     .. Local Arrays ..
INTEGER            ISAVE( 3 )
*     ..
*     .. External Functions ..
LOGICAL            LSAME
INTEGER            IDAMAX
DOUBLE PRECISION   DLAMCH
EXTERNAL           LSAME, IDAMAX, DLAMCH
*     ..
*     .. External Subroutines ..
EXTERNAL           DLACN2, DLATRS, DRSCL, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          ABS, MAX
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
INFO = 0
UPPER = LSAME( UPLO, 'U' )
IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -1
ELSE IF( N.LT.0 ) THEN
INFO = -2
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -4
ELSE IF( ANORM.LT.ZERO ) THEN
INFO = -5
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'DPOCON', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
RCOND = ZERO
IF( N.EQ.0 ) THEN
RCOND = ONE
RETURN
ELSE IF( ANORM.EQ.ZERO ) THEN
RETURN
END IF
*
SMLNUM = DLAMCH( 'Safe minimum' )
*
*     Estimate the 1-norm of inv(A).
*
KASE = 0
NORMIN = 'N'
10 CONTINUE
CALL DLACN2( N, WORK( N+1 ), WORK, IWORK, AINVNM, KASE, ISAVE )
IF( KASE.NE.0 ) THEN
IF( UPPER ) THEN
*
*           Multiply by inv(U').
*
CALL DLATRS( 'Upper', 'Transpose', 'Non-unit', NORMIN, N, A,
\$                   LDA, WORK, SCALEL, WORK( 2*N+1 ), INFO )
NORMIN = 'Y'
*
*           Multiply by inv(U).
*
CALL DLATRS( 'Upper', 'No transpose', 'Non-unit', NORMIN, N,
\$                   A, LDA, WORK, SCALEU, WORK( 2*N+1 ), INFO )
ELSE
*
*           Multiply by inv(L).
*
CALL DLATRS( 'Lower', 'No transpose', 'Non-unit', NORMIN, N,
\$                   A, LDA, WORK, SCALEL, WORK( 2*N+1 ), INFO )
NORMIN = 'Y'
*
*           Multiply by inv(L').
*
CALL DLATRS( 'Lower', 'Transpose', 'Non-unit', NORMIN, N, A,
\$                   LDA, WORK, SCALEU, WORK( 2*N+1 ), INFO )
END IF
*
*        Multiply by 1/SCALE if doing so will not cause overflow.
*
SCALE = SCALEL*SCALEU
IF( SCALE.NE.ONE ) THEN
IX = IDAMAX( N, WORK, 1 )
IF( SCALE.LT.ABS( WORK( IX ) )*SMLNUM .OR. SCALE.EQ.ZERO )
\$         GO TO 20
CALL DRSCL( N, SCALE, WORK, 1 )
END IF
GO TO 10
END IF
*
*     Compute the estimate of the reciprocal condition number.
*
IF( AINVNM.NE.ZERO )
\$   RCOND = ( ONE / AINVNM ) / ANORM
*
20 CONTINUE
RETURN
*
*     End of DPOCON
*
END

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