SPTTS2  - solve a tridiagonal system of the form A * X = B
       using the L*D*L' factorization of A computed by SPTTRF


SYNOPSIS

       SUBROUTINE SPTTS2( N, NRHS, D, E, B, LDB )

           INTEGER        LDB, N, NRHS

           REAL           B( LDB, * ), D( * ), E( * )


PURPOSE

       SPTTS2 solves a tridiagonal system of the form A * X  =  B
       using  the L*D*L' factorization of A computed by SPTTRF. D
       is a diagonal matrix specified in the vector  D,  L  is  a
       unit  bidiagonal  matrix whose subdiagonal is specified in
       the vector E, and X and B are N by NRHS matrices.


ARGUMENTS

       N       (input) INTEGER
               The order of the tridiagonal 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.

       D       (input) REAL array, dimension (N)
               The  n  diagonal elements of the diagonal matrix D
               from the L*D*L' factorization of A.

       E       (input) REAL array, dimension (N-1)
               The (n-1) subdiagonal elements of the unit bidiag­
               onal  factor L from the L*D*L' factorization of A.
               E can also be regarded as the superdiagonal of the
               unit  bidiagonal factor U from the factorization A
               = U'*D*U.

       B       (input/output) REAL array, dimension (LDB,NRHS)
               On entry, the right hand side vectors  B  for  the
               system of linear equations.  On exit, the solution
               vectors, X.

       LDB     (input) INTEGER
               The leading dimension of  the  array  B.   LDB  >=
               max(1,N).


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