sgtsv(3S)

NAME
     SGTSV - solve the equation  A*X = B,

SYNOPSIS
     SUBROUTINE SGTSV( N, NRHS, DL, D, DU, B, LDB, INFO )

         INTEGER       INFO, LDB, N, NRHS

         REAL          B( LDB, * ), D( * ), DL( * ), DU( * )

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
     SGTSV solves the equation A*X = B, where A is an n by n tridiagonal
     matrix, by Gaussian elimination with partial pivoting.

     Note that the equation  A'*X = B  may be solved by interchanging the
     order of the arguments DU and DL.


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.

     DL      (input/output) REAL array, dimension (N-1)
             On entry, DL must contain the (n-1) sub-diagonal elements of A.

             On exit, DL is overwritten by the (n-2) elements of the second
             super-diagonal of the upper triangular matrix U from the LU
             factorization of A, in DL(1), ..., DL(n-2).

     D       (input/output) REAL array, dimension (N)
             On entry, D must contain the diagonal elements of A.

             On exit, D is overwritten by the n diagonal elements of U.
     DU      (input/output) REAL array, dimension (N-1)
             On entry, DU must contain the (n-1) super-diagonal elements of A.

             On exit, DU is overwritten by the (n-1) elements of the first
             super-diagonal of U.

     B       (input/output) REAL array, dimension (LDB,NRHS)
             On entry, the N by NRHS matrix of 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, U(i,i) is exactly zero, 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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