sptsv(3S)

NAME
     SPTSV - compute 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

SYNOPSIS
     SUBROUTINE SPTSV( N, NRHS, D, E, B, LDB, INFO )

         INTEGER       INFO, LDB, N, NRHS

         REAL          B( LDB, * ), D( * ), E( * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

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.

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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