zpttrs(3S)

NAME
     ZPTTRS - solve a tridiagonal system of the form A * X = B using the
     factorization A = U'*D*U or A = L*D*L' computed by ZPTTRF

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

         CHARACTER      UPLO

         INTEGER        INFO, LDB, N, NRHS

         DOUBLE         PRECISION D( * )

         COMPLEX*16     B( LDB, * ), 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
     ZPTTRS solves a tridiagonal system of the form A * X = B using the
     factorization A = U'*D*U or A = L*D*L' computed by ZPTTRF. D is a
     diagonal matrix specified in the vector D, U (or L) is a unit bidiagonal
     matrix whose superdiagonal (subdiagonal) is specified in the vector E,
     and X and B are N by NRHS matrices.


ARGUMENTS
     UPLO    (input) CHARACTER*1
             Specifies the form of the factorization and whether the vector E
             is the superdiagonal of the upper bidiagonal factor U or the
             subdiagonal of the lower bidiagonal factor L.  = 'U':  A =
             U'*D*U, E is the superdiagonal of U
             = 'L':  A = L*D*L', E is the subdiagonal of L

     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
             factorization A = U'*D*U or A = L*D*L'.

     E       (input) COMPLEX*16 array, dimension (N-1)
             If UPLO = 'U', the (n-1) superdiagonal elements of the unit
             bidiagonal factor U from the factorization A = U'*D*U.  If UPLO =
             'L', the (n-1) subdiagonal elements of the unit bidiagonal factor
             L from the factorization A = L*D*L'.

     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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