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( * )


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 inter­
       changing 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 triangu­
               lar 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  ele­
               ments 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.

               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  ille­
               gal 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.


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