sptsv()

subroutine sptsv	(	integer	n,
		integer	nrhs,
		real, dimension( * )	d,
		real, dimension( * )	e,
		real, dimension( ldb, * )	b,
		integer	ldb,
		integer	info )

SPTSV computes the solution to system of linear equations A * X = B for PT matrices

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Purpose:

!>
!> SPTSV computes the solution to a real system of linear equations
!> A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
!> matrix, and X and B are N-by-NRHS matrices.
!>
!> A is factored as A = L*D*L**T, and the factored form of A is then
!> used to solve the system of equations.
!> 

Parameters

[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in]	NRHS	!> NRHS is INTEGER !> The number of right hand sides, i.e., the number of columns !> of the matrix B. NRHS >= 0. !>
[in,out]	D	!> D is REAL array, dimension (N) !> On entry, the n diagonal elements of the tridiagonal matrix !> A. On exit, the n diagonal elements of the diagonal matrix !> D from the factorization A = L*D*L**T. !>
[in,out]	E	!> E is REAL array, dimension (N-1) !> On entry, the (n-1) subdiagonal elements of the tridiagonal !> matrix A. On exit, the (n-1) subdiagonal elements of the !> unit bidiagonal factor L from the L*D*L**T factorization of !> A. (E can also be regarded as the superdiagonal of the unit !> bidiagonal factor U from the U**T*D*U factorization of A.) !>
[in,out]	B	!> B is REAL array, dimension (LDB,NRHS) !> On entry, the N-by-NRHS right hand side matrix B. !> On exit, if INFO = 0, the N-by-NRHS solution matrix X. !>
[in]	LDB	!> LDB is INTEGER !> The leading dimension of the array B. LDB >= max(1,N). !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !> > 0: if INFO = i, the leading principal minor of order i !> is not positive, and the solution has not been !> computed. The factorization has not been completed !> unless i = N. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 111 of file sptsv.f.

*
*  -- LAPACK driver routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      INTEGER            INFO, LDB, N, NRHS
*     ..
*     .. Array Arguments ..
      REAL               B( LDB, * ), D( * ), E( * )
*     ..
*
*  =====================================================================
*
*     .. External Subroutines ..
      EXTERNAL           spttrf, spttrs, xerbla
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          max
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
      info = 0
      IF( n.LT.0 ) THEN
         info = -1
      ELSE IF( nrhs.LT.0 ) THEN
         info = -2
      ELSE IF( ldb.LT.max( 1, n ) ) THEN
         info = -6
      END IF
      IF( info.NE.0 ) THEN
         CALL xerbla( 'SPTSV ', -info )
         RETURN
      END IF
*
*     Compute the L*D*L**T (or U**T*D*U) factorization of A.
*
      CALL spttrf( n, d, e, info )
      IF( info.EQ.0 ) THEN
*
*        Solve the system A*X = B, overwriting B with X.
*
         CALL spttrs( n, nrhs, d, e, b, ldb, info )
      END IF
      RETURN
*
*     End of SPTSV
*

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