*> \brief \b ZPTTRS * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download ZPTTRS + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE ZPTTRS( UPLO, N, NRHS, D, E, B, LDB, INFO ) * * .. Scalar Arguments .. * CHARACTER UPLO * INTEGER INFO, LDB, N, NRHS * .. * .. Array Arguments .. * DOUBLE PRECISION D( * ) * COMPLEX*16 B( LDB, * ), E( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> ZPTTRS solves a tridiagonal system of the form *> A * X = B *> using the factorization A = U**H *D* U or A = L*D*L**H computed by ZPTTRF. *> D is a diagonal matrix specified in the vector D, U (or L) is a unit *> bidiagonal matrix whose superdiagonal (subdiagonal) is specified in *> the vector E, and X and B are N by NRHS matrices. *> \endverbatim * * Arguments: * ========== * *> \param[in] UPLO *> \verbatim *> UPLO is CHARACTER*1 *> Specifies the form of the factorization and whether the *> vector E is the superdiagonal of the upper bidiagonal factor *> U or the subdiagonal of the lower bidiagonal factor L. *> = 'U': A = U**H *D*U, E is the superdiagonal of U *> = 'L': A = L*D*L**H, E is the subdiagonal of L *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The order of the tridiagonal matrix A. N >= 0. *> \endverbatim *> *> \param[in] NRHS *> \verbatim *> NRHS is INTEGER *> The number of right hand sides, i.e., the number of columns *> of the matrix B. NRHS >= 0. *> \endverbatim *> *> \param[in] D *> \verbatim *> D is DOUBLE PRECISION array, dimension (N) *> The n diagonal elements of the diagonal matrix D from the *> factorization A = U**H *D*U or A = L*D*L**H. *> \endverbatim *> *> \param[in] E *> \verbatim *> E is COMPLEX*16 array, dimension (N-1) *> If UPLO = 'U', the (n-1) superdiagonal elements of the unit *> bidiagonal factor U from the factorization A = U**H*D*U. *> If UPLO = 'L', the (n-1) subdiagonal elements of the unit *> bidiagonal factor L from the factorization A = L*D*L**H. *> \endverbatim *> *> \param[in,out] B *> \verbatim *> B is COMPLEX*16 array, dimension (LDB,NRHS) *> On entry, the right hand side vectors B for the system of *> linear equations. *> On exit, the solution vectors, X. *> \endverbatim *> *> \param[in] LDB *> \verbatim *> LDB is INTEGER *> The leading dimension of the array B. LDB >= max(1,N). *> \endverbatim *> *> \param[out] INFO *> \verbatim *> INFO is INTEGER *> = 0: successful exit *> < 0: if INFO = -k, the k-th argument had an illegal value *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date June 2016 * *> \ingroup complex16PTcomputational * * ===================================================================== SUBROUTINE ZPTTRS( UPLO, N, NRHS, D, E, B, LDB, INFO ) * * -- LAPACK computational routine (version 3.7.0) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * June 2016 * * .. Scalar Arguments .. CHARACTER UPLO INTEGER INFO, LDB, N, NRHS * .. * .. Array Arguments .. DOUBLE PRECISION D( * ) COMPLEX*16 B( LDB, * ), E( * ) * .. * * ===================================================================== * * .. Local Scalars .. LOGICAL UPPER INTEGER IUPLO, J, JB, NB * .. * .. External Functions .. INTEGER ILAENV EXTERNAL ILAENV * .. * .. External Subroutines .. EXTERNAL XERBLA, ZPTTS2 * .. * .. Intrinsic Functions .. INTRINSIC MAX, MIN * .. * .. Executable Statements .. * * Test the input arguments. * INFO = 0 UPPER = ( UPLO.EQ.'U' .OR. UPLO.EQ.'u' ) IF( .NOT.UPPER .AND. .NOT.( UPLO.EQ.'L' .OR. UPLO.EQ.'l' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( NRHS.LT.0 ) THEN INFO = -3 ELSE IF( LDB.LT.MAX( 1, N ) ) THEN INFO = -7 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'ZPTTRS', -INFO ) RETURN END IF * * Quick return if possible * IF( N.EQ.0 .OR. NRHS.EQ.0 ) \$ RETURN * * Determine the number of right-hand sides to solve at a time. * IF( NRHS.EQ.1 ) THEN NB = 1 ELSE NB = MAX( 1, ILAENV( 1, 'ZPTTRS', UPLO, N, NRHS, -1, -1 ) ) END IF * * Decode UPLO * IF( UPPER ) THEN IUPLO = 1 ELSE IUPLO = 0 END IF * IF( NB.GE.NRHS ) THEN CALL ZPTTS2( IUPLO, N, NRHS, D, E, B, LDB ) ELSE DO 10 J = 1, NRHS, NB JB = MIN( NRHS-J+1, NB ) CALL ZPTTS2( IUPLO, N, JB, D, E, B( 1, J ), LDB ) 10 CONTINUE END IF * RETURN * * End of ZPTTRS * END