CGTSV - solve the equation  A*X = B,


SYNOPSIS

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

           INTEGER       INFO, LDB, N, NRHS

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


PURPOSE

       CGTSV  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) COMPLEX array, dimension (N-1)
               On  entry,  DL  must contain the (n-1) subdiagonal
               elements of A.  On exit, DL is overwritten by  the
               (n-2)  elements of the second superdiagonal of the
               upper triangular matrix U from the  LU  factoriza­
               tion of A, in DL(1), ..., DL(n-2).

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

       B       (input/output) COMPLEX array, dimension (LDB,NRHS)
               On entry, the N-by-NRHS 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).

               = 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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