TESTING/EIG/cstt21.f(3)    Library Functions Manual    TESTING/EIG/cstt21.f(3)

NAME
       TESTING/EIG/cstt21.f

SYNOPSIS
   Functions/Subroutines
       subroutine cstt21 (n, kband, ad, ae, sd, se, u, ldu, work, rwork,
           result)
           CSTT21

Function/Subroutine Documentation
   subroutine cstt21 (integer n, integer kband, real, dimension( * ) ad, real,
       dimension( * ) ae, real, dimension( * ) sd, real, dimension( * ) se,
       complex, dimension( ldu, * ) u, integer ldu, complex, dimension( * )
       work, real, dimension( * ) rwork, real, dimension( 2 ) result)
       CSTT21

       Purpose:


            CSTT21  checks a decomposition of the form

               A = U S U**H

            where **H means conjugate transpose, A is real symmetric tridiagonal,
            U is unitary, and S is real and diagonal (if KBAND=0) or symmetric
            tridiagonal (if KBAND=1).  Two tests are performed:

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

               RESULT(2) = | I - U U**H | / ( n ulp )

       Parameters
           N

                     N is INTEGER
                     The size of the matrix.  If it is zero, CSTT21 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 REAL array, dimension (N)
                     The diagonal of the original (unfactored) matrix A.  A is
                     assumed to be real symmetric tridiagonal.

           AE

                     AE is REAL 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 REAL array, dimension (N)
                     The diagonal of the real (symmetric tri-) diagonal matrix S.

           SE

                     SE is REAL 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 COMPLEX array, dimension (LDU, N)
                     The unitary matrix in the decomposition.

           LDU

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

           WORK

                     WORK is COMPLEX array, dimension (N**2)

           RWORK

                     RWORK is REAL array, dimension (N)

           RESULT

                     RESULT is REAL 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 131 of file cstt21.f.

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

LAPACK                          Version 3.12.0         TESTING/EIG/cstt21.f(3)