SGTSV(3)       LAPACK routine of NEC Numeric Library Collection       SGTSV(3)



NAME
       SGTSV

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



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**T*X = B  may be solved by interchanging the
            order of the arguments DU and DL.




ARGUMENTS
           N         (input)
                     N is INTEGER
                     The order of the matrix A.  N >= 0.

           NRHS      (input)
                     NRHS is INTEGER
                     The number of right hand sides, i.e., the number of columns
                     of the matrix B.  NRHS >= 0.

           DL        (input/output)
                     DL is 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)
                     D is 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)
                     DU is 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)
                     B is 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)
                     LDB is INTEGER
                     The leading dimension of the array B.  LDB >= max(1,N).

           INFO      (output)
                     INFO is 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.



LAPACK routine                  31 October 2017                       SGTSV(3)