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

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