SUBROUTINE SPTSV( N, NRHS, D, E, B, LDB, INFO )
*
* -- LAPACK routine (version 3.1) --
* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
* November 2006
*
* .. Scalar Arguments ..
INTEGER INFO, LDB, N, NRHS
* ..
* .. Array Arguments ..
REAL B( LDB, * ), D( * ), E( * )
* ..
*
* 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.
*
* Arguments
* =========
*
* N (input) INTEGER
* The order of the matrix A. N >= 0.
*
* NRHS (input) INTEGER
* The number of right hand sides, i.e., the number of columns
* of the matrix B. NRHS >= 0.
*
* D (input/output) 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.
*
* E (input/output) 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.)
*
* B (input/output) 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.
*
* LDB (input) INTEGER
* The leading dimension of the array B. LDB >= max(1,N).
*
* INFO (output) INTEGER
* = 0: successful exit
* < 0: if INFO = -i, the i-th argument had an illegal value
* > 0: if INFO = i, the leading minor of order i is not
* positive definite, and the solution has not been
* computed. The factorization has not been completed
* unless i = N.
*
* =====================================================================
*
* .. 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' (or U'*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
*
END