*> \brief \b ZSYTRF * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download ZSYTRF + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE ZSYTRF( UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO ) * * .. Scalar Arguments .. * CHARACTER UPLO * INTEGER INFO, LDA, LWORK, N * .. * .. Array Arguments .. * INTEGER IPIV( * ) * COMPLEX*16 A( LDA, * ), WORK( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> ZSYTRF computes the factorization of a complex symmetric matrix A *> using the Bunch-Kaufman diagonal pivoting method. The form of the *> factorization is *> *> A = U*D*U**T or A = L*D*L**T *> *> where U (or L) is a product of permutation and unit upper (lower) *> triangular matrices, and D is symmetric and block diagonal with *> with 1-by-1 and 2-by-2 diagonal blocks. *> *> This is the blocked version of the algorithm, calling Level 3 BLAS. *> \endverbatim * * Arguments: * ========== * *> \param[in] UPLO *> \verbatim *> UPLO is CHARACTER*1 *> = 'U': Upper triangle of A is stored; *> = 'L': Lower triangle of A is stored. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The order of the matrix A. N >= 0. *> \endverbatim *> *> \param[in,out] A *> \verbatim *> A is COMPLEX*16 array, dimension (LDA,N) *> On entry, the symmetric matrix A. If UPLO = 'U', the leading *> N-by-N upper triangular part of A contains the upper *> triangular part of the matrix A, and the strictly lower *> triangular part of A is not referenced. If UPLO = 'L', the *> leading N-by-N lower triangular part of A contains the lower *> triangular part of the matrix A, and the strictly upper *> triangular part of A is not referenced. *> *> On exit, the block diagonal matrix D and the multipliers used *> to obtain the factor U or L (see below for further details). *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> The leading dimension of the array A. LDA >= max(1,N). *> \endverbatim *> *> \param[out] IPIV *> \verbatim *> IPIV is INTEGER array, dimension (N) *> Details of the interchanges and the block structure of D. *> If IPIV(k) > 0, then rows and columns k and IPIV(k) were *> interchanged and D(k,k) is a 1-by-1 diagonal block. *> If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and *> columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k) *> is a 2-by-2 diagonal block. If UPLO = 'L' and IPIV(k) = *> IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were *> interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block. *> \endverbatim *> *> \param[out] WORK *> \verbatim *> WORK is COMPLEX*16 array, dimension (MAX(1,LWORK)) *> On exit, if INFO = 0, WORK(1) returns the optimal LWORK. *> \endverbatim *> *> \param[in] LWORK *> \verbatim *> LWORK is INTEGER *> The length of WORK. LWORK >=1. For best performance *> LWORK >= N*NB, where NB is the block size returned by ILAENV. *> *> If LWORK = -1, then a workspace query is assumed; the routine *> only calculates the optimal size of the WORK array, returns *> this value as the first entry of the WORK array, and no error *> message related to LWORK is issued by XERBLA. *> \endverbatim *> *> \param[out] INFO *> \verbatim *> INFO is INTEGER *> = 0: successful exit *> < 0: if INFO = -i, the i-th argument had an illegal value *> > 0: if INFO = i, D(i,i) is exactly zero. The factorization *> has been completed, but the block diagonal matrix D is *> exactly singular, and division by zero will occur if it *> is used to solve a system of equations. *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date December 2016 * *> \ingroup complex16SYcomputational * *> \par Further Details: * ===================== *> *> \verbatim *> *> If UPLO = 'U', then A = U*D*U**T, where *> U = P(n)*U(n)* ... *P(k)U(k)* ..., *> i.e., U is a product of terms P(k)*U(k), where k decreases from n to *> 1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 *> and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as *> defined by IPIV(k), and U(k) is a unit upper triangular matrix, such *> that if the diagonal block D(k) is of order s (s = 1 or 2), then *> *> ( I v 0 ) k-s *> U(k) = ( 0 I 0 ) s *> ( 0 0 I ) n-k *> k-s s n-k *> *> If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k). *> If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k), *> and A(k,k), and v overwrites A(1:k-2,k-1:k). *> *> If UPLO = 'L', then A = L*D*L**T, where *> L = P(1)*L(1)* ... *P(k)*L(k)* ..., *> i.e., L is a product of terms P(k)*L(k), where k increases from 1 to *> n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 *> and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as *> defined by IPIV(k), and L(k) is a unit lower triangular matrix, such *> that if the diagonal block D(k) is of order s (s = 1 or 2), then *> *> ( I 0 0 ) k-1 *> L(k) = ( 0 I 0 ) s *> ( 0 v I ) n-k-s+1 *> k-1 s n-k-s+1 *> *> If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k). *> If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k), *> and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1). *> \endverbatim *> * ===================================================================== SUBROUTINE ZSYTRF( UPLO, N, A, LDA, IPIV, WORK, LWORK, 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..-- * December 2016 * * .. Scalar Arguments .. CHARACTER UPLO INTEGER INFO, LDA, LWORK, N * .. * .. Array Arguments .. INTEGER IPIV( * ) COMPLEX*16 A( LDA, * ), WORK( * ) * .. * * ===================================================================== * * .. Local Scalars .. LOGICAL LQUERY, UPPER INTEGER IINFO, IWS, J, K, KB, LDWORK, LWKOPT, NB, NBMIN * .. * .. External Functions .. LOGICAL LSAME INTEGER ILAENV EXTERNAL LSAME, ILAENV * .. * .. External Subroutines .. EXTERNAL XERBLA, ZLASYF, ZSYTF2 * .. * .. Intrinsic Functions .. INTRINSIC MAX * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 UPPER = LSAME( UPLO, 'U' ) LQUERY = ( LWORK.EQ.-1 ) IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -4 ELSE IF( LWORK.LT.1 .AND. .NOT.LQUERY ) THEN INFO = -7 END IF * IF( INFO.EQ.0 ) THEN * * Determine the block size * NB = ILAENV( 1, 'ZSYTRF', UPLO, N, -1, -1, -1 ) LWKOPT = N*NB WORK( 1 ) = LWKOPT END IF * IF( INFO.NE.0 ) THEN CALL XERBLA( 'ZSYTRF', -INFO ) RETURN ELSE IF( LQUERY ) THEN RETURN END IF * NBMIN = 2 LDWORK = N IF( NB.GT.1 .AND. NB.LT.N ) THEN IWS = LDWORK*NB IF( LWORK.LT.IWS ) THEN NB = MAX( LWORK / LDWORK, 1 ) NBMIN = MAX( 2, ILAENV( 2, 'ZSYTRF', UPLO, N, -1, -1, -1 ) ) END IF ELSE IWS = 1 END IF IF( NB.LT.NBMIN ) \$ NB = N * IF( UPPER ) THEN * * Factorize A as U*D*U**T using the upper triangle of A * * K is the main loop index, decreasing from N to 1 in steps of * KB, where KB is the number of columns factorized by ZLASYF; * KB is either NB or NB-1, or K for the last block * K = N 10 CONTINUE * * If K < 1, exit from loop * IF( K.LT.1 ) \$ GO TO 40 * IF( K.GT.NB ) THEN * * Factorize columns k-kb+1:k of A and use blocked code to * update columns 1:k-kb * CALL ZLASYF( UPLO, K, NB, KB, A, LDA, IPIV, WORK, N, IINFO ) ELSE * * Use unblocked code to factorize columns 1:k of A * CALL ZSYTF2( UPLO, K, A, LDA, IPIV, IINFO ) KB = K END IF * * Set INFO on the first occurrence of a zero pivot * IF( INFO.EQ.0 .AND. IINFO.GT.0 ) \$ INFO = IINFO * * Decrease K and return to the start of the main loop * K = K - KB GO TO 10 * ELSE * * Factorize A as L*D*L**T using the lower triangle of A * * K is the main loop index, increasing from 1 to N in steps of * KB, where KB is the number of columns factorized by ZLASYF; * KB is either NB or NB-1, or N-K+1 for the last block * K = 1 20 CONTINUE * * If K > N, exit from loop * IF( K.GT.N ) \$ GO TO 40 * IF( K.LE.N-NB ) THEN * * Factorize columns k:k+kb-1 of A and use blocked code to * update columns k+kb:n * CALL ZLASYF( UPLO, N-K+1, NB, KB, A( K, K ), LDA, IPIV( K ), \$ WORK, N, IINFO ) ELSE * * Use unblocked code to factorize columns k:n of A * CALL ZSYTF2( UPLO, N-K+1, A( K, K ), LDA, IPIV( K ), IINFO ) KB = N - K + 1 END IF * * Set INFO on the first occurrence of a zero pivot * IF( INFO.EQ.0 .AND. IINFO.GT.0 ) \$ INFO = IINFO + K - 1 * * Adjust IPIV * DO 30 J = K, K + KB - 1 IF( IPIV( J ).GT.0 ) THEN IPIV( J ) = IPIV( J ) + K - 1 ELSE IPIV( J ) = IPIV( J ) - K + 1 END IF 30 CONTINUE * * Increase K and return to the start of the main loop * K = K + KB GO TO 20 * END IF * 40 CONTINUE WORK( 1 ) = LWKOPT RETURN * * End of ZSYTRF * END