686 lines
25 KiB
Fortran
686 lines
25 KiB
Fortran
*> \brief \b DLA_GERFSX_EXTENDED improves the computed solution to a system of linear equations for general matrices by performing extra-precise iterative refinement and provides error bounds and backward error estimates for the solution.
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download DLA_GERFSX_EXTENDED + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dla_gerfsx_extended.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dla_gerfsx_extended.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dla_gerfsx_extended.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE DLA_GERFSX_EXTENDED( PREC_TYPE, TRANS_TYPE, N, NRHS, A,
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* LDA, AF, LDAF, IPIV, COLEQU, C, B,
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* LDB, Y, LDY, BERR_OUT, N_NORMS,
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* ERRS_N, ERRS_C, RES, AYB, DY,
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* Y_TAIL, RCOND, ITHRESH, RTHRESH,
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* DZ_UB, IGNORE_CWISE, INFO )
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*
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* .. Scalar Arguments ..
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* INTEGER INFO, LDA, LDAF, LDB, LDY, N, NRHS, PREC_TYPE,
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* $ TRANS_TYPE, N_NORMS, ITHRESH
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* LOGICAL COLEQU, IGNORE_CWISE
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* DOUBLE PRECISION RTHRESH, DZ_UB
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* ..
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* .. Array Arguments ..
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* INTEGER IPIV( * )
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* DOUBLE PRECISION A( LDA, * ), AF( LDAF, * ), B( LDB, * ),
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* $ Y( LDY, * ), RES( * ), DY( * ), Y_TAIL( * )
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* DOUBLE PRECISION C( * ), AYB( * ), RCOND, BERR_OUT( * ),
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* $ ERRS_N( NRHS, * ), ERRS_C( NRHS, * )
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*>
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*> DLA_GERFSX_EXTENDED improves the computed solution to a system of
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*> linear equations by performing extra-precise iterative refinement
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*> and provides error bounds and backward error estimates for the solution.
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*> This subroutine is called by DGERFSX to perform iterative refinement.
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*> In addition to normwise error bound, the code provides maximum
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*> componentwise error bound if possible. See comments for ERRS_N
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*> and ERRS_C for details of the error bounds. Note that this
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*> subroutine is only responsible for setting the second fields of
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*> ERRS_N and ERRS_C.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in] PREC_TYPE
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*> \verbatim
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*> PREC_TYPE is INTEGER
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*> Specifies the intermediate precision to be used in refinement.
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*> The value is defined by ILAPREC(P) where P is a CHARACTER and P
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*> = 'S': Single
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*> = 'D': Double
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*> = 'I': Indigenous
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*> = 'X' or 'E': Extra
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*> \endverbatim
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*>
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*> \param[in] TRANS_TYPE
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*> \verbatim
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*> TRANS_TYPE is INTEGER
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*> Specifies the transposition operation on A.
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*> The value is defined by ILATRANS(T) where T is a CHARACTER and T
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*> = 'N': No transpose
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*> = 'T': Transpose
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*> = 'C': Conjugate transpose
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*> \endverbatim
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*>
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*> \param[in] N
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*> \verbatim
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*> N is INTEGER
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*> The number of linear equations, i.e., the order of the
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*> matrix A. N >= 0.
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*> \endverbatim
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*>
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*> \param[in] NRHS
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*> \verbatim
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*> NRHS is INTEGER
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*> The number of right-hand-sides, i.e., the number of columns of the
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*> matrix B.
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*> \endverbatim
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*>
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*> \param[in] A
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*> \verbatim
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*> A is DOUBLE PRECISION array, dimension (LDA,N)
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*> On entry, the N-by-N matrix A.
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*> \endverbatim
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*>
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*> \param[in] LDA
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*> \verbatim
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*> LDA is INTEGER
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*> The leading dimension of the array A. LDA >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in] AF
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*> \verbatim
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*> AF is DOUBLE PRECISION array, dimension (LDAF,N)
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*> The factors L and U from the factorization
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*> A = P*L*U as computed by DGETRF.
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*> \endverbatim
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*>
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*> \param[in] LDAF
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*> \verbatim
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*> LDAF is INTEGER
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*> The leading dimension of the array AF. LDAF >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in] IPIV
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*> \verbatim
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*> IPIV is INTEGER array, dimension (N)
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*> The pivot indices from the factorization A = P*L*U
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*> as computed by DGETRF; row i of the matrix was interchanged
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*> with row IPIV(i).
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*> \endverbatim
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*>
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*> \param[in] COLEQU
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*> \verbatim
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*> COLEQU is LOGICAL
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*> If .TRUE. then column equilibration was done to A before calling
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*> this routine. This is needed to compute the solution and error
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*> bounds correctly.
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*> \endverbatim
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*>
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*> \param[in] C
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*> \verbatim
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*> C is DOUBLE PRECISION array, dimension (N)
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*> The column scale factors for A. If COLEQU = .FALSE., C
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*> is not accessed. If C is input, each element of C should be a power
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*> of the radix to ensure a reliable solution and error estimates.
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*> Scaling by powers of the radix does not cause rounding errors unless
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*> the result underflows or overflows. Rounding errors during scaling
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*> lead to refining with a matrix that is not equivalent to the
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*> input matrix, producing error estimates that may not be
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*> reliable.
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*> \endverbatim
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*>
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*> \param[in] B
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*> \verbatim
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*> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
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*> The right-hand-side matrix B.
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*> \endverbatim
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*>
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*> \param[in] LDB
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*> \verbatim
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*> LDB is INTEGER
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*> The leading dimension of the array B. LDB >= max(1,N).
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*> \endverbatim
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*>
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*> \param[in,out] Y
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*> \verbatim
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*> Y is DOUBLE PRECISION array, dimension (LDY,NRHS)
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*> On entry, the solution matrix X, as computed by DGETRS.
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*> On exit, the improved solution matrix Y.
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*> \endverbatim
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*>
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*> \param[in] LDY
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*> \verbatim
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*> LDY is INTEGER
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*> The leading dimension of the array Y. LDY >= max(1,N).
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*> \endverbatim
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*>
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*> \param[out] BERR_OUT
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*> \verbatim
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*> BERR_OUT is DOUBLE PRECISION array, dimension (NRHS)
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*> On exit, BERR_OUT(j) contains the componentwise relative backward
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*> error for right-hand-side j from the formula
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*> max(i) ( abs(RES(i)) / ( abs(op(A_s))*abs(Y) + abs(B_s) )(i) )
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*> where abs(Z) is the componentwise absolute value of the matrix
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*> or vector Z. This is computed by DLA_LIN_BERR.
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*> \endverbatim
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*>
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*> \param[in] N_NORMS
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*> \verbatim
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*> N_NORMS is INTEGER
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*> Determines which error bounds to return (see ERRS_N
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*> and ERRS_C).
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*> If N_NORMS >= 1 return normwise error bounds.
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*> If N_NORMS >= 2 return componentwise error bounds.
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*> \endverbatim
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*>
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*> \param[in,out] ERRS_N
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*> \verbatim
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*> ERRS_N is DOUBLE PRECISION array, dimension (NRHS, N_ERR_BNDS)
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*> For each right-hand side, this array contains information about
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*> various error bounds and condition numbers corresponding to the
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*> normwise relative error, which is defined as follows:
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*>
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*> Normwise relative error in the ith solution vector:
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*> max_j (abs(XTRUE(j,i) - X(j,i)))
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*> ------------------------------
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*> max_j abs(X(j,i))
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*>
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*> The array is indexed by the type of error information as described
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*> below. There currently are up to three pieces of information
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*> returned.
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*>
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*> The first index in ERRS_N(i,:) corresponds to the ith
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*> right-hand side.
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*>
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*> The second index in ERRS_N(:,err) contains the following
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*> three fields:
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*> err = 1 "Trust/don't trust" boolean. Trust the answer if the
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*> reciprocal condition number is less than the threshold
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*> sqrt(n) * slamch('Epsilon').
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*>
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*> err = 2 "Guaranteed" error bound: The estimated forward error,
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*> almost certainly within a factor of 10 of the true error
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*> so long as the next entry is greater than the threshold
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*> sqrt(n) * slamch('Epsilon'). This error bound should only
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*> be trusted if the previous boolean is true.
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*>
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*> err = 3 Reciprocal condition number: Estimated normwise
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*> reciprocal condition number. Compared with the threshold
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*> sqrt(n) * slamch('Epsilon') to determine if the error
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*> estimate is "guaranteed". These reciprocal condition
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*> numbers are 1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some
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*> appropriately scaled matrix Z.
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*> Let Z = S*A, where S scales each row by a power of the
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*> radix so all absolute row sums of Z are approximately 1.
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*>
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*> This subroutine is only responsible for setting the second field
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*> above.
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*> See Lapack Working Note 165 for further details and extra
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*> cautions.
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*> \endverbatim
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*>
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*> \param[in,out] ERRS_C
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*> \verbatim
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*> ERRS_C is DOUBLE PRECISION array, dimension (NRHS, N_ERR_BNDS)
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*> For each right-hand side, this array contains information about
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*> various error bounds and condition numbers corresponding to the
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*> componentwise relative error, which is defined as follows:
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*>
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*> Componentwise relative error in the ith solution vector:
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*> abs(XTRUE(j,i) - X(j,i))
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*> max_j ----------------------
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*> abs(X(j,i))
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*>
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*> The array is indexed by the right-hand side i (on which the
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*> componentwise relative error depends), and the type of error
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*> information as described below. There currently are up to three
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*> pieces of information returned for each right-hand side. If
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*> componentwise accuracy is not requested (PARAMS(3) = 0.0), then
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*> ERRS_C is not accessed. If N_ERR_BNDS < 3, then at most
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*> the first (:,N_ERR_BNDS) entries are returned.
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*>
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*> The first index in ERRS_C(i,:) corresponds to the ith
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*> right-hand side.
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*>
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*> The second index in ERRS_C(:,err) contains the following
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*> three fields:
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*> err = 1 "Trust/don't trust" boolean. Trust the answer if the
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*> reciprocal condition number is less than the threshold
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*> sqrt(n) * slamch('Epsilon').
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*>
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*> err = 2 "Guaranteed" error bound: The estimated forward error,
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*> almost certainly within a factor of 10 of the true error
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*> so long as the next entry is greater than the threshold
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*> sqrt(n) * slamch('Epsilon'). This error bound should only
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*> be trusted if the previous boolean is true.
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*>
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*> err = 3 Reciprocal condition number: Estimated componentwise
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*> reciprocal condition number. Compared with the threshold
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*> sqrt(n) * slamch('Epsilon') to determine if the error
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*> estimate is "guaranteed". These reciprocal condition
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*> numbers are 1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some
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*> appropriately scaled matrix Z.
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*> Let Z = S*(A*diag(x)), where x is the solution for the
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*> current right-hand side and S scales each row of
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*> A*diag(x) by a power of the radix so all absolute row
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*> sums of Z are approximately 1.
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*>
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*> This subroutine is only responsible for setting the second field
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*> above.
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*> See Lapack Working Note 165 for further details and extra
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*> cautions.
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*> \endverbatim
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*>
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*> \param[in] RES
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*> \verbatim
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*> RES is DOUBLE PRECISION array, dimension (N)
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*> Workspace to hold the intermediate residual.
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*> \endverbatim
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*>
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*> \param[in] AYB
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*> \verbatim
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*> AYB is DOUBLE PRECISION array, dimension (N)
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*> Workspace. This can be the same workspace passed for Y_TAIL.
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*> \endverbatim
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*>
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*> \param[in] DY
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*> \verbatim
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*> DY is DOUBLE PRECISION array, dimension (N)
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*> Workspace to hold the intermediate solution.
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*> \endverbatim
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*>
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*> \param[in] Y_TAIL
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*> \verbatim
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*> Y_TAIL is DOUBLE PRECISION array, dimension (N)
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*> Workspace to hold the trailing bits of the intermediate solution.
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*> \endverbatim
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*>
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*> \param[in] RCOND
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*> \verbatim
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*> RCOND is DOUBLE PRECISION
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*> Reciprocal scaled condition number. This is an estimate of the
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*> reciprocal Skeel condition number of the matrix A after
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*> equilibration (if done). If this is less than the machine
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*> precision (in particular, if it is zero), the matrix is singular
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*> to working precision. Note that the error may still be small even
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*> if this number is very small and the matrix appears ill-
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*> conditioned.
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*> \endverbatim
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*>
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*> \param[in] ITHRESH
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*> \verbatim
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*> ITHRESH is INTEGER
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*> The maximum number of residual computations allowed for
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*> refinement. The default is 10. For 'aggressive' set to 100 to
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*> permit convergence using approximate factorizations or
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*> factorizations other than LU. If the factorization uses a
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*> technique other than Gaussian elimination, the guarantees in
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*> ERRS_N and ERRS_C may no longer be trustworthy.
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*> \endverbatim
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*>
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*> \param[in] RTHRESH
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*> \verbatim
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*> RTHRESH is DOUBLE PRECISION
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*> Determines when to stop refinement if the error estimate stops
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*> decreasing. Refinement will stop when the next solution no longer
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*> satisfies norm(dx_{i+1}) < RTHRESH * norm(dx_i) where norm(Z) is
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*> the infinity norm of Z. RTHRESH satisfies 0 < RTHRESH <= 1. The
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*> default value is 0.5. For 'aggressive' set to 0.9 to permit
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*> convergence on extremely ill-conditioned matrices. See LAWN 165
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*> for more details.
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*> \endverbatim
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*>
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*> \param[in] DZ_UB
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*> \verbatim
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*> DZ_UB is DOUBLE PRECISION
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*> Determines when to start considering componentwise convergence.
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*> Componentwise convergence is only considered after each component
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*> of the solution Y is stable, which we define as the relative
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*> change in each component being less than DZ_UB. The default value
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*> is 0.25, requiring the first bit to be stable. See LAWN 165 for
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*> more details.
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*> \endverbatim
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*>
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*> \param[in] IGNORE_CWISE
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*> \verbatim
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*> IGNORE_CWISE is LOGICAL
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*> If .TRUE. then ignore componentwise convergence. Default value
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*> is .FALSE..
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*> \endverbatim
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*>
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*> \param[out] INFO
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*> \verbatim
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*> INFO is INTEGER
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*> = 0: Successful exit.
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*> < 0: if INFO = -i, the ith argument to DGETRS had an illegal
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*> value
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \ingroup doubleGEcomputational
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*
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* =====================================================================
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SUBROUTINE DLA_GERFSX_EXTENDED( PREC_TYPE, TRANS_TYPE, N, NRHS, A,
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$ LDA, AF, LDAF, IPIV, COLEQU, C, B,
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$ LDB, Y, LDY, BERR_OUT, N_NORMS,
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$ ERRS_N, ERRS_C, RES, AYB, DY,
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$ Y_TAIL, RCOND, ITHRESH, RTHRESH,
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$ DZ_UB, IGNORE_CWISE, INFO )
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*
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* -- LAPACK computational routine --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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*
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* .. Scalar Arguments ..
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INTEGER INFO, LDA, LDAF, LDB, LDY, N, NRHS, PREC_TYPE,
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$ TRANS_TYPE, N_NORMS, ITHRESH
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LOGICAL COLEQU, IGNORE_CWISE
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DOUBLE PRECISION RTHRESH, DZ_UB
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* ..
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* .. Array Arguments ..
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INTEGER IPIV( * )
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DOUBLE PRECISION A( LDA, * ), AF( LDAF, * ), B( LDB, * ),
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$ Y( LDY, * ), RES( * ), DY( * ), Y_TAIL( * )
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DOUBLE PRECISION C( * ), AYB( * ), RCOND, BERR_OUT( * ),
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$ ERRS_N( NRHS, * ), ERRS_C( NRHS, * )
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* ..
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*
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* =====================================================================
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*
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* .. Local Scalars ..
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CHARACTER TRANS
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INTEGER CNT, I, J, X_STATE, Z_STATE, Y_PREC_STATE
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DOUBLE PRECISION YK, DYK, YMIN, NORMY, NORMX, NORMDX, DXRAT,
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$ DZRAT, PREVNORMDX, PREV_DZ_Z, DXRATMAX,
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$ DZRATMAX, DX_X, DZ_Z, FINAL_DX_X, FINAL_DZ_Z,
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$ EPS, HUGEVAL, INCR_THRESH
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LOGICAL INCR_PREC
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* ..
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* .. Parameters ..
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INTEGER UNSTABLE_STATE, WORKING_STATE, CONV_STATE,
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$ NOPROG_STATE, BASE_RESIDUAL, EXTRA_RESIDUAL,
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$ EXTRA_Y
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PARAMETER ( UNSTABLE_STATE = 0, WORKING_STATE = 1,
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$ CONV_STATE = 2, NOPROG_STATE = 3 )
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PARAMETER ( BASE_RESIDUAL = 0, EXTRA_RESIDUAL = 1,
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$ EXTRA_Y = 2 )
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INTEGER FINAL_NRM_ERR_I, FINAL_CMP_ERR_I, BERR_I
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INTEGER RCOND_I, NRM_RCOND_I, NRM_ERR_I, CMP_RCOND_I
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INTEGER CMP_ERR_I, PIV_GROWTH_I
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PARAMETER ( FINAL_NRM_ERR_I = 1, FINAL_CMP_ERR_I = 2,
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$ BERR_I = 3 )
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PARAMETER ( RCOND_I = 4, NRM_RCOND_I = 5, NRM_ERR_I = 6 )
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PARAMETER ( CMP_RCOND_I = 7, CMP_ERR_I = 8,
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$ PIV_GROWTH_I = 9 )
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INTEGER LA_LINRX_ITREF_I, LA_LINRX_ITHRESH_I,
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$ LA_LINRX_CWISE_I
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PARAMETER ( LA_LINRX_ITREF_I = 1,
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$ LA_LINRX_ITHRESH_I = 2 )
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PARAMETER ( LA_LINRX_CWISE_I = 3 )
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INTEGER LA_LINRX_TRUST_I, LA_LINRX_ERR_I,
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$ LA_LINRX_RCOND_I
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PARAMETER ( LA_LINRX_TRUST_I = 1, LA_LINRX_ERR_I = 2 )
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PARAMETER ( LA_LINRX_RCOND_I = 3 )
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* ..
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* .. External Subroutines ..
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EXTERNAL DAXPY, DCOPY, DGETRS, DGEMV, BLAS_DGEMV_X,
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$ BLAS_DGEMV2_X, DLA_GEAMV, DLA_WWADDW, DLAMCH,
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$ CHLA_TRANSTYPE, DLA_LIN_BERR
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DOUBLE PRECISION DLAMCH
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CHARACTER CHLA_TRANSTYPE
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC ABS, MAX, MIN
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* ..
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* .. Executable Statements ..
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*
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IF ( INFO.NE.0 ) RETURN
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TRANS = CHLA_TRANSTYPE(TRANS_TYPE)
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EPS = DLAMCH( 'Epsilon' )
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HUGEVAL = DLAMCH( 'Overflow' )
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* Force HUGEVAL to Inf
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HUGEVAL = HUGEVAL * HUGEVAL
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* Using HUGEVAL may lead to spurious underflows.
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INCR_THRESH = DBLE( N ) * EPS
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*
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DO J = 1, NRHS
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Y_PREC_STATE = EXTRA_RESIDUAL
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IF ( Y_PREC_STATE .EQ. EXTRA_Y ) THEN
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DO I = 1, N
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Y_TAIL( I ) = 0.0D+0
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END DO
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END IF
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DXRAT = 0.0D+0
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DXRATMAX = 0.0D+0
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DZRAT = 0.0D+0
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DZRATMAX = 0.0D+0
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FINAL_DX_X = HUGEVAL
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FINAL_DZ_Z = HUGEVAL
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PREVNORMDX = HUGEVAL
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PREV_DZ_Z = HUGEVAL
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DZ_Z = HUGEVAL
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DX_X = HUGEVAL
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X_STATE = WORKING_STATE
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Z_STATE = UNSTABLE_STATE
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INCR_PREC = .FALSE.
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DO CNT = 1, ITHRESH
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*
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* Compute residual RES = B_s - op(A_s) * Y,
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* op(A) = A, A**T, or A**H depending on TRANS (and type).
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*
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CALL DCOPY( N, B( 1, J ), 1, RES, 1 )
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IF ( Y_PREC_STATE .EQ. BASE_RESIDUAL ) THEN
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CALL DGEMV( TRANS, N, N, -1.0D+0, A, LDA, Y( 1, J ), 1,
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$ 1.0D+0, RES, 1 )
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ELSE IF ( Y_PREC_STATE .EQ. EXTRA_RESIDUAL ) THEN
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CALL BLAS_DGEMV_X( TRANS_TYPE, N, N, -1.0D+0, A, LDA,
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$ Y( 1, J ), 1, 1.0D+0, RES, 1, PREC_TYPE )
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ELSE
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CALL BLAS_DGEMV2_X( TRANS_TYPE, N, N, -1.0D+0, A, LDA,
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$ Y( 1, J ), Y_TAIL, 1, 1.0D+0, RES, 1, PREC_TYPE )
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END IF
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! XXX: RES is no longer needed.
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CALL DCOPY( N, RES, 1, DY, 1 )
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CALL DGETRS( TRANS, N, 1, AF, LDAF, IPIV, DY, N, INFO )
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*
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* Calculate relative changes DX_X, DZ_Z and ratios DXRAT, DZRAT.
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*
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NORMX = 0.0D+0
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NORMY = 0.0D+0
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NORMDX = 0.0D+0
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DZ_Z = 0.0D+0
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YMIN = HUGEVAL
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*
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DO I = 1, N
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YK = ABS( Y( I, J ) )
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DYK = ABS( DY( I ) )
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IF ( YK .NE. 0.0D+0 ) THEN
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DZ_Z = MAX( DZ_Z, DYK / YK )
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ELSE IF ( DYK .NE. 0.0D+0 ) THEN
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DZ_Z = HUGEVAL
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END IF
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YMIN = MIN( YMIN, YK )
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NORMY = MAX( NORMY, YK )
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IF ( COLEQU ) THEN
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NORMX = MAX( NORMX, YK * C( I ) )
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NORMDX = MAX( NORMDX, DYK * C( I ) )
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ELSE
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NORMX = NORMY
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NORMDX = MAX( NORMDX, DYK )
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END IF
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END DO
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IF ( NORMX .NE. 0.0D+0 ) THEN
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DX_X = NORMDX / NORMX
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ELSE IF ( NORMDX .EQ. 0.0D+0 ) THEN
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DX_X = 0.0D+0
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ELSE
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DX_X = HUGEVAL
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END IF
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DXRAT = NORMDX / PREVNORMDX
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DZRAT = DZ_Z / PREV_DZ_Z
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*
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* Check termination criteria
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*
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IF (.NOT.IGNORE_CWISE
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$ .AND. YMIN*RCOND .LT. INCR_THRESH*NORMY
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$ .AND. Y_PREC_STATE .LT. EXTRA_Y)
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$ INCR_PREC = .TRUE.
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IF ( X_STATE .EQ. NOPROG_STATE .AND. DXRAT .LE. RTHRESH )
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$ X_STATE = WORKING_STATE
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IF ( X_STATE .EQ. WORKING_STATE ) THEN
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IF ( DX_X .LE. EPS ) THEN
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X_STATE = CONV_STATE
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ELSE IF ( DXRAT .GT. RTHRESH ) THEN
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IF ( Y_PREC_STATE .NE. EXTRA_Y ) THEN
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INCR_PREC = .TRUE.
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ELSE
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X_STATE = NOPROG_STATE
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END IF
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ELSE
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IF ( DXRAT .GT. DXRATMAX ) DXRATMAX = DXRAT
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END IF
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IF ( X_STATE .GT. WORKING_STATE ) FINAL_DX_X = DX_X
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END IF
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IF ( Z_STATE .EQ. UNSTABLE_STATE .AND. DZ_Z .LE. DZ_UB )
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$ Z_STATE = WORKING_STATE
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IF ( Z_STATE .EQ. NOPROG_STATE .AND. DZRAT .LE. RTHRESH )
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$ Z_STATE = WORKING_STATE
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IF ( Z_STATE .EQ. WORKING_STATE ) THEN
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IF ( DZ_Z .LE. EPS ) THEN
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Z_STATE = CONV_STATE
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ELSE IF ( DZ_Z .GT. DZ_UB ) THEN
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Z_STATE = UNSTABLE_STATE
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DZRATMAX = 0.0D+0
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FINAL_DZ_Z = HUGEVAL
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ELSE IF ( DZRAT .GT. RTHRESH ) THEN
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IF ( Y_PREC_STATE .NE. EXTRA_Y ) THEN
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INCR_PREC = .TRUE.
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ELSE
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Z_STATE = NOPROG_STATE
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END IF
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ELSE
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IF ( DZRAT .GT. DZRATMAX ) DZRATMAX = DZRAT
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END IF
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IF ( Z_STATE .GT. WORKING_STATE ) FINAL_DZ_Z = DZ_Z
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END IF
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*
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* Exit if both normwise and componentwise stopped working,
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* but if componentwise is unstable, let it go at least two
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* iterations.
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*
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IF ( X_STATE.NE.WORKING_STATE ) THEN
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IF ( IGNORE_CWISE) GOTO 666
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IF ( Z_STATE.EQ.NOPROG_STATE .OR. Z_STATE.EQ.CONV_STATE )
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$ GOTO 666
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IF ( Z_STATE.EQ.UNSTABLE_STATE .AND. CNT.GT.1 ) GOTO 666
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END IF
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IF ( INCR_PREC ) THEN
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INCR_PREC = .FALSE.
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Y_PREC_STATE = Y_PREC_STATE + 1
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DO I = 1, N
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Y_TAIL( I ) = 0.0D+0
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END DO
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END IF
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PREVNORMDX = NORMDX
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PREV_DZ_Z = DZ_Z
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*
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* Update solution.
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*
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IF ( Y_PREC_STATE .LT. EXTRA_Y ) THEN
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CALL DAXPY( N, 1.0D+0, DY, 1, Y( 1, J ), 1 )
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ELSE
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CALL DLA_WWADDW( N, Y( 1, J ), Y_TAIL, DY )
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END IF
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END DO
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* Target of "IF (Z_STOP .AND. X_STOP)". Sun's f77 won't EXIT.
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666 CONTINUE
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*
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* Set final_* when cnt hits ithresh.
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*
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IF ( X_STATE .EQ. WORKING_STATE ) FINAL_DX_X = DX_X
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IF ( Z_STATE .EQ. WORKING_STATE ) FINAL_DZ_Z = DZ_Z
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*
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* Compute error bounds
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*
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IF (N_NORMS .GE. 1) THEN
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ERRS_N( J, LA_LINRX_ERR_I ) = FINAL_DX_X / (1 - DXRATMAX)
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END IF
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IF ( N_NORMS .GE. 2 ) THEN
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ERRS_C( J, LA_LINRX_ERR_I ) = FINAL_DZ_Z / (1 - DZRATMAX)
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END IF
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*
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* Compute componentwise relative backward error from formula
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* max(i) ( abs(R(i)) / ( abs(op(A_s))*abs(Y) + abs(B_s) )(i) )
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* where abs(Z) is the componentwise absolute value of the matrix
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* or vector Z.
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*
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* Compute residual RES = B_s - op(A_s) * Y,
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* op(A) = A, A**T, or A**H depending on TRANS (and type).
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*
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CALL DCOPY( N, B( 1, J ), 1, RES, 1 )
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CALL DGEMV( TRANS, N, N, -1.0D+0, A, LDA, Y(1,J), 1, 1.0D+0,
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$ RES, 1 )
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DO I = 1, N
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AYB( I ) = ABS( B( I, J ) )
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END DO
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*
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* Compute abs(op(A_s))*abs(Y) + abs(B_s).
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*
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CALL DLA_GEAMV ( TRANS_TYPE, N, N, 1.0D+0,
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$ A, LDA, Y(1, J), 1, 1.0D+0, AYB, 1 )
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CALL DLA_LIN_BERR ( N, N, 1, RES, AYB, BERR_OUT( J ) )
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*
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* End of loop for each RHS.
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*
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END DO
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*
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RETURN
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*
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* End of DLA_GERFSX_EXTENDED
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*
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END
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