dpttrs(3S)

NAME
     DPTTRS - solve a tridiagonal system of the form A * X = B using the
     L*D*L' factorization of A computed by DPTTRF

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

         INTEGER        INFO, LDB, N, NRHS

         DOUBLE         PRECISION 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
     DPTTRS solves a tridiagonal system of the form A * X = B using the L*D*L'
     factorization of A computed by DPTTRF. D is a diagonal matrix specified
     in the vector D, L is a unit bidiagonal matrix whose subdiagonal is
     specified in the vector E, and X and B are N by NRHS matrices.


ARGUMENTS
     N       (input) INTEGER
             The order of the tridiagonal 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) DOUBLE PRECISION array, dimension (N)
             The n diagonal elements of the diagonal matrix D from the L*D*L'
             factorization of A.

     E       (input) DOUBLE PRECISION array, dimension (N-1)
             The (n-1) subdiagonal elements of the unit bidiagonal factor L
             from the L*D*L' factorization of A.  E can also be regarded as
             the superdiagonal of the unit bidiagonal factor U from the
             factorization A = U'*D*U.

     B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
             On entry, the right hand side vectors B for the system of linear
             equations.  On exit, the solution vectors, X.
     LDB     (input) INTEGER
             The leading dimension of the array B.  LDB >= max(1,N).

     INFO    (output) INTEGER
             = 0: successful exit
             < 0: if INFO = -k, the k-th argument had an illegal value

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

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