543 lines
		
	
	
		
			18 KiB
		
	
	
	
		
			Fortran
		
	
	
	
			
		
		
	
	
			543 lines
		
	
	
		
			18 KiB
		
	
	
	
		
			Fortran
		
	
	
	
| *> \brief <b> DPBSVX computes the solution to system of linear equations A * X = B for OTHER matrices</b>
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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 DPBSVX + dependencies
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| *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dpbsvx.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/dpbsvx.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/dpbsvx.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 DPBSVX( FACT, UPLO, N, KD, NRHS, AB, LDAB, AFB, LDAFB,
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| *                          EQUED, S, B, LDB, X, LDX, RCOND, FERR, BERR,
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| *                          WORK, IWORK, INFO )
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| *
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| *       .. Scalar Arguments ..
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| *       CHARACTER          EQUED, FACT, UPLO
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| *       INTEGER            INFO, KD, LDAB, LDAFB, LDB, LDX, N, NRHS
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| *       DOUBLE PRECISION   RCOND
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| *       ..
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| *       .. Array Arguments ..
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| *       INTEGER            IWORK( * )
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| *       DOUBLE PRECISION   AB( LDAB, * ), AFB( LDAFB, * ), B( LDB, * ),
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| *      $                   BERR( * ), FERR( * ), S( * ), WORK( * ),
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| *      $                   X( LDX, * )
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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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| *> DPBSVX uses the Cholesky factorization A = U**T*U or A = L*L**T to
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| *> compute the solution to a real system of linear equations
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| *>    A * X = B,
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| *> where A is an N-by-N symmetric positive definite band matrix and X
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| *> and B are N-by-NRHS matrices.
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| *>
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| *> Error bounds on the solution and a condition estimate are also
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| *> provided.
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| *> \endverbatim
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| *
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| *> \par Description:
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| *  =================
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| *>
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| *> \verbatim
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| *>
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| *> The following steps are performed:
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| *>
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| *> 1. If FACT = 'E', real scaling factors are computed to equilibrate
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| *>    the system:
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| *>       diag(S) * A * diag(S) * inv(diag(S)) * X = diag(S) * B
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| *>    Whether or not the system will be equilibrated depends on the
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| *>    scaling of the matrix A, but if equilibration is used, A is
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| *>    overwritten by diag(S)*A*diag(S) and B by diag(S)*B.
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| *>
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| *> 2. If FACT = 'N' or 'E', the Cholesky decomposition is used to
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| *>    factor the matrix A (after equilibration if FACT = 'E') as
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| *>       A = U**T * U,  if UPLO = 'U', or
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| *>       A = L * L**T,  if UPLO = 'L',
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| *>    where U is an upper triangular band matrix, and L is a lower
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| *>    triangular band matrix.
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| *>
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| *> 3. If the leading principal minor of order i is not positive,
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| *>    then the routine returns with INFO = i. Otherwise, the factored
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| *>    form of A is used to estimate the condition number of the matrix
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| *>    A.  If the reciprocal of the condition number is less than machine
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| *>    precision, INFO = N+1 is returned as a warning, but the routine
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| *>    still goes on to solve for X and compute error bounds as
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| *>    described below.
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| *>
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| *> 4. The system of equations is solved for X using the factored form
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| *>    of A.
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| *>
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| *> 5. Iterative refinement is applied to improve the computed solution
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| *>    matrix and calculate error bounds and backward error estimates
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| *>    for it.
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| *>
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| *> 6. If equilibration was used, the matrix X is premultiplied by
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| *>    diag(S) so that it solves the original system before
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| *>    equilibration.
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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] FACT
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| *> \verbatim
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| *>          FACT is CHARACTER*1
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| *>          Specifies whether or not the factored form of the matrix A is
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| *>          supplied on entry, and if not, whether the matrix A should be
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| *>          equilibrated before it is factored.
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| *>          = 'F':  On entry, AFB contains the factored form of A.
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| *>                  If EQUED = 'Y', the matrix A has been equilibrated
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| *>                  with scaling factors given by S.  AB and AFB will not
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| *>                  be modified.
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| *>          = 'N':  The matrix A will be copied to AFB and factored.
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| *>          = 'E':  The matrix A will be equilibrated if necessary, then
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| *>                  copied to AFB and factored.
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| *> \endverbatim
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| *>
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| *> \param[in] UPLO
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| *> \verbatim
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| *>          UPLO is CHARACTER*1
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| *>          = 'U':  Upper triangle of A is stored;
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| *>          = 'L':  Lower triangle of A is stored.
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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] KD
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| *> \verbatim
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| *>          KD is INTEGER
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| *>          The number of superdiagonals of the matrix A if UPLO = 'U',
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| *>          or the number of subdiagonals if UPLO = 'L'.  KD >= 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
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| *>          of the matrices B and X.  NRHS >= 0.
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| *> \endverbatim
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| *>
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| *> \param[in,out] AB
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| *> \verbatim
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| *>          AB is DOUBLE PRECISION array, dimension (LDAB,N)
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| *>          On entry, the upper or lower triangle of the symmetric band
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| *>          matrix A, stored in the first KD+1 rows of the array, except
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| *>          if FACT = 'F' and EQUED = 'Y', then A must contain the
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| *>          equilibrated matrix diag(S)*A*diag(S).  The j-th column of A
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| *>          is stored in the j-th column of the array AB as follows:
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| *>          if UPLO = 'U', AB(KD+1+i-j,j) = A(i,j) for max(1,j-KD)<=i<=j;
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| *>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(N,j+KD).
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| *>          See below for further details.
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| *>
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| *>          On exit, if FACT = 'E' and EQUED = 'Y', A is overwritten by
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| *>          diag(S)*A*diag(S).
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| *> \endverbatim
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| *>
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| *> \param[in] LDAB
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| *> \verbatim
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| *>          LDAB is INTEGER
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| *>          The leading dimension of the array A.  LDAB >= KD+1.
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| *> \endverbatim
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| *>
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| *> \param[in,out] AFB
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| *> \verbatim
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| *>          AFB is DOUBLE PRECISION array, dimension (LDAFB,N)
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| *>          If FACT = 'F', then AFB is an input argument and on entry
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| *>          contains the triangular factor U or L from the Cholesky
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| *>          factorization A = U**T*U or A = L*L**T of the band matrix
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| *>          A, in the same storage format as A (see AB).  If EQUED = 'Y',
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| *>          then AFB is the factored form of the equilibrated matrix A.
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| *>
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| *>          If FACT = 'N', then AFB is an output argument and on exit
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| *>          returns the triangular factor U or L from the Cholesky
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| *>          factorization A = U**T*U or A = L*L**T.
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| *>
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| *>          If FACT = 'E', then AFB is an output argument and on exit
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| *>          returns the triangular factor U or L from the Cholesky
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| *>          factorization A = U**T*U or A = L*L**T of the equilibrated
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| *>          matrix A (see the description of A for the form of the
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| *>          equilibrated matrix).
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| *> \endverbatim
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| *>
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| *> \param[in] LDAFB
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| *> \verbatim
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| *>          LDAFB is INTEGER
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| *>          The leading dimension of the array AFB.  LDAFB >= KD+1.
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| *> \endverbatim
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| *>
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| *> \param[in,out] EQUED
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| *> \verbatim
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| *>          EQUED is CHARACTER*1
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| *>          Specifies the form of equilibration that was done.
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| *>          = 'N':  No equilibration (always true if FACT = 'N').
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| *>          = 'Y':  Equilibration was done, i.e., A has been replaced by
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| *>                  diag(S) * A * diag(S).
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| *>          EQUED is an input argument if FACT = 'F'; otherwise, it is an
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| *>          output argument.
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| *> \endverbatim
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| *>
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| *> \param[in,out] S
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| *> \verbatim
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| *>          S is DOUBLE PRECISION array, dimension (N)
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| *>          The scale factors for A; not accessed if EQUED = 'N'.  S is
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| *>          an input argument if FACT = 'F'; otherwise, S is an output
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| *>          argument.  If FACT = 'F' and EQUED = 'Y', each element of S
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| *>          must be positive.
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| *> \endverbatim
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| *>
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| *> \param[in,out] B
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| *> \verbatim
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| *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
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| *>          On entry, the N-by-NRHS right hand side matrix B.
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| *>          On exit, if EQUED = 'N', B is not modified; if EQUED = 'Y',
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| *>          B is overwritten by diag(S) * 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[out] X
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| *> \verbatim
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| *>          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
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| *>          If INFO = 0 or INFO = N+1, the N-by-NRHS solution matrix X to
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| *>          the original system of equations.  Note that if EQUED = 'Y',
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| *>          A and B are modified on exit, and the solution to the
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| *>          equilibrated system is inv(diag(S))*X.
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| *> \endverbatim
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| *>
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| *> \param[in] LDX
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| *> \verbatim
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| *>          LDX is INTEGER
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| *>          The leading dimension of the array X.  LDX >= max(1,N).
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| *> \endverbatim
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| *>
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| *> \param[out] RCOND
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| *> \verbatim
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| *>          RCOND is DOUBLE PRECISION
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| *>          The estimate of the reciprocal condition number of the matrix
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| *>          A after equilibration (if done).  If RCOND is less than the
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| *>          machine precision (in particular, if RCOND = 0), the matrix
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| *>          is singular to working precision.  This condition is
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| *>          indicated by a return code of INFO > 0.
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| *> \endverbatim
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| *>
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| *> \param[out] FERR
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| *> \verbatim
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| *>          FERR is DOUBLE PRECISION array, dimension (NRHS)
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| *>          The estimated forward error bound for each solution vector
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| *>          X(j) (the j-th column of the solution matrix X).
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| *>          If XTRUE is the true solution corresponding to X(j), FERR(j)
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| *>          is an estimated upper bound for the magnitude of the largest
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| *>          element in (X(j) - XTRUE) divided by the magnitude of the
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| *>          largest element in X(j).  The estimate is as reliable as
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| *>          the estimate for RCOND, and is almost always a slight
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| *>          overestimate of the true error.
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| *> \endverbatim
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| *>
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| *> \param[out] BERR
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| *> \verbatim
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| *>          BERR is DOUBLE PRECISION array, dimension (NRHS)
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| *>          The componentwise relative backward error of each solution
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| *>          vector X(j) (i.e., the smallest relative change in
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| *>          any element of A or B that makes X(j) an exact solution).
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| *> \endverbatim
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| *>
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| *> \param[out] WORK
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| *> \verbatim
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| *>          WORK is DOUBLE PRECISION array, dimension (3*N)
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| *> \endverbatim
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| *>
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| *> \param[out] IWORK
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| *> \verbatim
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| *>          IWORK is INTEGER array, dimension (N)
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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 i-th argument had an illegal value
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| *>          > 0:  if INFO = i, and i is
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| *>                <= N:  the leading principal minor of order i of A
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| *>                       is not positive, so the factorization could not
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| *>                       be completed, and the solution has not been
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| *>                       computed. RCOND = 0 is returned.
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| *>                = N+1: U is nonsingular, but RCOND is less than machine
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| *>                       precision, meaning that the matrix is singular
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| *>                       to working precision.  Nevertheless, the
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| *>                       solution and error bounds are computed because
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| *>                       there are a number of situations where the
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| *>                       computed solution can be more accurate than the
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| *>                       value of RCOND would suggest.
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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 doubleOTHERsolve
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| *
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| *> \par Further Details:
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| *  =====================
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| *>
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| *> \verbatim
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| *>
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| *>  The band storage scheme is illustrated by the following example, when
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| *>  N = 6, KD = 2, and UPLO = 'U':
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| *>
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| *>  Two-dimensional storage of the symmetric matrix A:
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| *>
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| *>     a11  a12  a13
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| *>          a22  a23  a24
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| *>               a33  a34  a35
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| *>                    a44  a45  a46
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| *>                         a55  a56
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| *>     (aij=conjg(aji))         a66
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| *>
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| *>  Band storage of the upper triangle of A:
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| *>
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| *>      *    *   a13  a24  a35  a46
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| *>      *   a12  a23  a34  a45  a56
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| *>     a11  a22  a33  a44  a55  a66
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| *>
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| *>  Similarly, if UPLO = 'L' the format of A is as follows:
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| *>
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| *>     a11  a22  a33  a44  a55  a66
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| *>     a21  a32  a43  a54  a65   *
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| *>     a31  a42  a53  a64   *    *
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| *>
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| *>  Array elements marked * are not used by the routine.
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| *> \endverbatim
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| *>
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| *  =====================================================================
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|       SUBROUTINE DPBSVX( FACT, UPLO, N, KD, NRHS, AB, LDAB, AFB, LDAFB,
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|      $                   EQUED, S, B, LDB, X, LDX, RCOND, FERR, BERR,
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|      $                   WORK, IWORK, INFO )
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| *
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| *  -- LAPACK driver 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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|       CHARACTER          EQUED, FACT, UPLO
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|       INTEGER            INFO, KD, LDAB, LDAFB, LDB, LDX, N, NRHS
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|       DOUBLE PRECISION   RCOND
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| *     ..
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| *     .. Array Arguments ..
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|       INTEGER            IWORK( * )
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|       DOUBLE PRECISION   AB( LDAB, * ), AFB( LDAFB, * ), B( LDB, * ),
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|      $                   BERR( * ), FERR( * ), S( * ), WORK( * ),
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|      $                   X( LDX, * )
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| *     ..
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| *
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| *  =====================================================================
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| *
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| *     .. Parameters ..
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|       DOUBLE PRECISION   ZERO, ONE
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|       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
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| *     ..
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| *     .. Local Scalars ..
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|       LOGICAL            EQUIL, NOFACT, RCEQU, UPPER
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|       INTEGER            I, INFEQU, J, J1, J2
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|       DOUBLE PRECISION   AMAX, ANORM, BIGNUM, SCOND, SMAX, SMIN, SMLNUM
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| *     ..
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| *     .. External Functions ..
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|       LOGICAL            LSAME
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|       DOUBLE PRECISION   DLAMCH, DLANSB
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|       EXTERNAL           LSAME, DLAMCH, DLANSB
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| *     ..
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| *     .. External Subroutines ..
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|       EXTERNAL           DCOPY, DLACPY, DLAQSB, DPBCON, DPBEQU, DPBRFS,
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|      $                   DPBTRF, DPBTRS, XERBLA
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| *     ..
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| *     .. Intrinsic Functions ..
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|       INTRINSIC          MAX, MIN
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| *     ..
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| *     .. Executable Statements ..
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| *
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|       INFO = 0
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|       NOFACT = LSAME( FACT, 'N' )
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|       EQUIL = LSAME( FACT, 'E' )
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|       UPPER = LSAME( UPLO, 'U' )
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|       IF( NOFACT .OR. EQUIL ) THEN
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|          EQUED = 'N'
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|          RCEQU = .FALSE.
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|       ELSE
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|          RCEQU = LSAME( EQUED, 'Y' )
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|          SMLNUM = DLAMCH( 'Safe minimum' )
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|          BIGNUM = ONE / SMLNUM
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|       END IF
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| *
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| *     Test the input parameters.
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| *
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|       IF( .NOT.NOFACT .AND. .NOT.EQUIL .AND. .NOT.LSAME( FACT, 'F' ) )
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|      $     THEN
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|          INFO = -1
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|       ELSE IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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|          INFO = -2
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|       ELSE IF( N.LT.0 ) THEN
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|          INFO = -3
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|       ELSE IF( KD.LT.0 ) THEN
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|          INFO = -4
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|       ELSE IF( NRHS.LT.0 ) THEN
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|          INFO = -5
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|       ELSE IF( LDAB.LT.KD+1 ) THEN
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|          INFO = -7
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|       ELSE IF( LDAFB.LT.KD+1 ) THEN
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|          INFO = -9
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|       ELSE IF( LSAME( FACT, 'F' ) .AND. .NOT.
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|      $         ( RCEQU .OR. LSAME( EQUED, 'N' ) ) ) THEN
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|          INFO = -10
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|       ELSE
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|          IF( RCEQU ) THEN
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|             SMIN = BIGNUM
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|             SMAX = ZERO
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|             DO 10 J = 1, N
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|                SMIN = MIN( SMIN, S( J ) )
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|                SMAX = MAX( SMAX, S( J ) )
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|    10       CONTINUE
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|             IF( SMIN.LE.ZERO ) THEN
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|                INFO = -11
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|             ELSE IF( N.GT.0 ) THEN
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|                SCOND = MAX( SMIN, SMLNUM ) / MIN( SMAX, BIGNUM )
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|             ELSE
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|                SCOND = ONE
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|             END IF
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|          END IF
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|          IF( INFO.EQ.0 ) THEN
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|             IF( LDB.LT.MAX( 1, N ) ) THEN
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|                INFO = -13
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|             ELSE IF( LDX.LT.MAX( 1, N ) ) THEN
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|                INFO = -15
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|             END IF
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|          END IF
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|       END IF
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| *
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|       IF( INFO.NE.0 ) THEN
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|          CALL XERBLA( 'DPBSVX', -INFO )
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|          RETURN
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|       END IF
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| *
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|       IF( EQUIL ) THEN
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| *
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| *        Compute row and column scalings to equilibrate the matrix A.
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| *
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|          CALL DPBEQU( UPLO, N, KD, AB, LDAB, S, SCOND, AMAX, INFEQU )
 | |
|          IF( INFEQU.EQ.0 ) THEN
 | |
| *
 | |
| *           Equilibrate the matrix.
 | |
| *
 | |
|             CALL DLAQSB( UPLO, N, KD, AB, LDAB, S, SCOND, AMAX, EQUED )
 | |
|             RCEQU = LSAME( EQUED, 'Y' )
 | |
|          END IF
 | |
|       END IF
 | |
| *
 | |
| *     Scale the right-hand side.
 | |
| *
 | |
|       IF( RCEQU ) THEN
 | |
|          DO 30 J = 1, NRHS
 | |
|             DO 20 I = 1, N
 | |
|                B( I, J ) = S( I )*B( I, J )
 | |
|    20       CONTINUE
 | |
|    30    CONTINUE
 | |
|       END IF
 | |
| *
 | |
|       IF( NOFACT .OR. EQUIL ) THEN
 | |
| *
 | |
| *        Compute the Cholesky factorization A = U**T *U or A = L*L**T.
 | |
| *
 | |
|          IF( UPPER ) THEN
 | |
|             DO 40 J = 1, N
 | |
|                J1 = MAX( J-KD, 1 )
 | |
|                CALL DCOPY( J-J1+1, AB( KD+1-J+J1, J ), 1,
 | |
|      $                     AFB( KD+1-J+J1, J ), 1 )
 | |
|    40       CONTINUE
 | |
|          ELSE
 | |
|             DO 50 J = 1, N
 | |
|                J2 = MIN( J+KD, N )
 | |
|                CALL DCOPY( J2-J+1, AB( 1, J ), 1, AFB( 1, J ), 1 )
 | |
|    50       CONTINUE
 | |
|          END IF
 | |
| *
 | |
|          CALL DPBTRF( UPLO, N, KD, AFB, LDAFB, INFO )
 | |
| *
 | |
| *        Return if INFO is non-zero.
 | |
| *
 | |
|          IF( INFO.GT.0 )THEN
 | |
|             RCOND = ZERO
 | |
|             RETURN
 | |
|          END IF
 | |
|       END IF
 | |
| *
 | |
| *     Compute the norm of the matrix A.
 | |
| *
 | |
|       ANORM = DLANSB( '1', UPLO, N, KD, AB, LDAB, WORK )
 | |
| *
 | |
| *     Compute the reciprocal of the condition number of A.
 | |
| *
 | |
|       CALL DPBCON( UPLO, N, KD, AFB, LDAFB, ANORM, RCOND, WORK, IWORK,
 | |
|      $             INFO )
 | |
| *
 | |
| *     Compute the solution matrix X.
 | |
| *
 | |
|       CALL DLACPY( 'Full', N, NRHS, B, LDB, X, LDX )
 | |
|       CALL DPBTRS( UPLO, N, KD, NRHS, AFB, LDAFB, X, LDX, INFO )
 | |
| *
 | |
| *     Use iterative refinement to improve the computed solution and
 | |
| *     compute error bounds and backward error estimates for it.
 | |
| *
 | |
|       CALL DPBRFS( UPLO, N, KD, NRHS, AB, LDAB, AFB, LDAFB, B, LDB, X,
 | |
|      $             LDX, FERR, BERR, WORK, IWORK, INFO )
 | |
| *
 | |
| *     Transform the solution matrix X to a solution of the original
 | |
| *     system.
 | |
| *
 | |
|       IF( RCEQU ) THEN
 | |
|          DO 70 J = 1, NRHS
 | |
|             DO 60 I = 1, N
 | |
|                X( I, J ) = S( I )*X( I, J )
 | |
|    60       CONTINUE
 | |
|    70    CONTINUE
 | |
|          DO 80 J = 1, NRHS
 | |
|             FERR( J ) = FERR( J ) / SCOND
 | |
|    80    CONTINUE
 | |
|       END IF
 | |
| *
 | |
| *     Set INFO = N+1 if the matrix is singular to working precision.
 | |
| *
 | |
|       IF( RCOND.LT.DLAMCH( 'Epsilon' ) )
 | |
|      $   INFO = N + 1
 | |
| *
 | |
|       RETURN
 | |
| *
 | |
| *     End of DPBSVX
 | |
| *
 | |
|       END
 |