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Annotation of rpl/lapack/lapack/dptsv.f, revision 1.8

1.1       bertrand    1:       SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )
                      2: *
1.8     ! bertrand    3: *  -- LAPACK routine (version 3.3.1) --
1.1       bertrand    4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                      5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8     ! bertrand    6: *  -- April 2011                                                      --
1.1       bertrand    7: *
                      8: *     .. Scalar Arguments ..
                      9:       INTEGER            INFO, LDB, N, NRHS
                     10: *     ..
                     11: *     .. Array Arguments ..
                     12:       DOUBLE PRECISION   B( LDB, * ), D( * ), E( * )
                     13: *     ..
                     14: *
                     15: *  Purpose
                     16: *  =======
                     17: *
                     18: *  DPTSV computes the solution to a real system of linear equations
                     19: *  A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
                     20: *  matrix, and X and B are N-by-NRHS matrices.
                     21: *
                     22: *  A is factored as A = L*D*L**T, and the factored form of A is then
                     23: *  used to solve the system of equations.
                     24: *
                     25: *  Arguments
                     26: *  =========
                     27: *
                     28: *  N       (input) INTEGER
                     29: *          The order of the matrix A.  N >= 0.
                     30: *
                     31: *  NRHS    (input) INTEGER
                     32: *          The number of right hand sides, i.e., the number of columns
                     33: *          of the matrix B.  NRHS >= 0.
                     34: *
                     35: *  D       (input/output) DOUBLE PRECISION array, dimension (N)
                     36: *          On entry, the n diagonal elements of the tridiagonal matrix
                     37: *          A.  On exit, the n diagonal elements of the diagonal matrix
                     38: *          D from the factorization A = L*D*L**T.
                     39: *
                     40: *  E       (input/output) DOUBLE PRECISION array, dimension (N-1)
                     41: *          On entry, the (n-1) subdiagonal elements of the tridiagonal
                     42: *          matrix A.  On exit, the (n-1) subdiagonal elements of the
                     43: *          unit bidiagonal factor L from the L*D*L**T factorization of
                     44: *          A.  (E can also be regarded as the superdiagonal of the unit
                     45: *          bidiagonal factor U from the U**T*D*U factorization of A.)
                     46: *
                     47: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
                     48: *          On entry, the N-by-NRHS right hand side matrix B.
                     49: *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
                     50: *
                     51: *  LDB     (input) INTEGER
                     52: *          The leading dimension of the array B.  LDB >= max(1,N).
                     53: *
                     54: *  INFO    (output) INTEGER
                     55: *          = 0:  successful exit
                     56: *          < 0:  if INFO = -i, the i-th argument had an illegal value
                     57: *          > 0:  if INFO = i, the leading minor of order i is not
                     58: *                positive definite, and the solution has not been
                     59: *                computed.  The factorization has not been completed
                     60: *                unless i = N.
                     61: *
                     62: *  =====================================================================
                     63: *
                     64: *     .. External Subroutines ..
                     65:       EXTERNAL           DPTTRF, DPTTRS, XERBLA
                     66: *     ..
                     67: *     .. Intrinsic Functions ..
                     68:       INTRINSIC          MAX
                     69: *     ..
                     70: *     .. Executable Statements ..
                     71: *
                     72: *     Test the input parameters.
                     73: *
                     74:       INFO = 0
                     75:       IF( N.LT.0 ) THEN
                     76:          INFO = -1
                     77:       ELSE IF( NRHS.LT.0 ) THEN
                     78:          INFO = -2
                     79:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
                     80:          INFO = -6
                     81:       END IF
                     82:       IF( INFO.NE.0 ) THEN
                     83:          CALL XERBLA( 'DPTSV ', -INFO )
                     84:          RETURN
                     85:       END IF
                     86: *
1.8     ! bertrand   87: *     Compute the L*D*L**T (or U**T*D*U) factorization of A.
1.1       bertrand   88: *
                     89:       CALL DPTTRF( N, D, E, INFO )
                     90:       IF( INFO.EQ.0 ) THEN
                     91: *
                     92: *        Solve the system A*X = B, overwriting B with X.
                     93: *
                     94:          CALL DPTTRS( N, NRHS, D, E, B, LDB, INFO )
                     95:       END IF
                     96:       RETURN
                     97: *
                     98: *     End of DPTSV
                     99: *
                    100:       END