SGTSV (3lapack)

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

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

  B       (input/output) REAL 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).

  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.