TESTING/EIG/dstt21.f(3)    Library Functions Manual    TESTING/EIG/dstt21.f(3)

NAME
       TESTING/EIG/dstt21.f

SYNOPSIS
   Functions/Subroutines
       subroutine dstt21 (n, kband, ad, ae, sd, se, u, ldu, work, result)
           DSTT21

Function/Subroutine Documentation
   subroutine dstt21 (integer n, integer kband, double precision, dimension( *
       ) ad, double precision, dimension( * ) ae, double precision, dimension(
       * ) sd, double precision, dimension( * ) se, double precision,
       dimension( ldu, * ) u, integer ldu, double precision, dimension( * )
       work, double precision, dimension( 2 ) result)
       DSTT21

       Purpose:


            DSTT21 checks a decomposition of the form

               A = U S U'

            where ' means transpose, A is symmetric tridiagonal, U is orthogonal,
            and S is diagonal (if KBAND=0) or symmetric tridiagonal (if KBAND=1).
            Two tests are performed:

               RESULT(1) = | A - U S U' | / ( |A| n ulp )

               RESULT(2) = | I - UU' | / ( n ulp )

       Parameters
           N

                     N is INTEGER
                     The size of the matrix.  If it is zero, DSTT21 does nothing.
                     It must be at least zero.

           KBAND

                     KBAND is INTEGER
                     The bandwidth of the matrix S.  It may only be zero or one.
                     If zero, then S is diagonal, and SE is not referenced.  If
                     one, then S is symmetric tri-diagonal.

           AD

                     AD is DOUBLE PRECISION array, dimension (N)
                     The diagonal of the original (unfactored) matrix A.  A is
                     assumed to be symmetric tridiagonal.

           AE

                     AE is DOUBLE PRECISION array, dimension (N-1)
                     The off-diagonal of the original (unfactored) matrix A.  A
                     is assumed to be symmetric tridiagonal.  AE(1) is the (1,2)
                     and (2,1) element, AE(2) is the (2,3) and (3,2) element, etc.

           SD

                     SD is DOUBLE PRECISION array, dimension (N)
                     The diagonal of the (symmetric tri-) diagonal matrix S.

           SE

                     SE is DOUBLE PRECISION array, dimension (N-1)
                     The off-diagonal of the (symmetric tri-) diagonal matrix S.
                     Not referenced if KBSND=0.  If KBAND=1, then AE(1) is the
                     (1,2) and (2,1) element, SE(2) is the (2,3) and (3,2)
                     element, etc.

           U

                     U is DOUBLE PRECISION array, dimension (LDU, N)
                     The orthogonal matrix in the decomposition.

           LDU

                     LDU is INTEGER
                     The leading dimension of U.  LDU must be at least N.

           WORK

                     WORK is DOUBLE PRECISION array, dimension (N*(N+1))

           RESULT

                     RESULT is DOUBLE PRECISION array, dimension (2)
                     The values computed by the two tests described above.  The
                     values are currently limited to 1/ulp, to avoid overflow.
                     RESULT(1) is always modified.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Definition at line 125 of file dstt21.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

LAPACK                          Version 3.12.0         TESTING/EIG/dstt21.f(3)