zstt21.f - Man Page

TESTING/EIG/zstt21.f

Synopsis

Functions/Subroutines

subroutine zstt21 (n, kband, ad, ae, sd, se, u, ldu, work, rwork, result)
ZSTT21

Function/Subroutine Documentation

subroutine zstt21 (integer n, integer kband, double precision, dimension( * ) ad, double precision, dimension( * ) ae, double precision, dimension( * ) sd, double precision, dimension( * ) se, complex*16, dimension( ldu, * ) u, integer ldu, complex*16, dimension( * ) work, double precision, dimension( * ) rwork, double precision, dimension( 2 ) result)

ZSTT21

Purpose:

 ZSTT21  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, ZSTT21 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 real 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 real (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 COMPLEX*16 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*16 array, dimension (N**2)

RWORK

          RWORK is DOUBLE PRECISION array, dimension (N)

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 131 of file zstt21.f.

Author

Generated automatically by Doxygen for LAPACK from the source code.

Referenced By

The man page zstt21(3) is an alias of zstt21.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK