zstt22()

subroutine zstt22	(	integer	n,
		integer	m,
		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( ldwork, * )	work,
		integer	ldwork,
		double precision, dimension( * )	rwork,
		double precision, dimension( 2 )	result
	)

ZSTT22

Purpose:

 ZSTT22  checks a set of M eigenvalues and eigenvectors,

     A U = U S

 where A is Hermitian tridiagonal, the columns of U are unitary,
 and S is diagonal (if KBAND=0) or Hermitian tridiagonal (if KBAND=1).
 Two tests are performed:

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

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

Parameters

[in]	N	N is INTEGER The size of the matrix. If it is zero, ZSTT22 does nothing. It must be at least zero.
[in]	M	M is INTEGER The number of eigenpairs to check. If it is zero, ZSTT22 does nothing. It must be at least zero.
[in]	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 Hermitian tri-diagonal.
[in]	AD	AD is DOUBLE PRECISION array, dimension (N) The diagonal of the original (unfactored) matrix A. A is assumed to be Hermitian tridiagonal.
[in]	AE	AE is DOUBLE PRECISION array, dimension (N) The off-diagonal of the original (unfactored) matrix A. A is assumed to be Hermitian tridiagonal. AE(1) is ignored, AE(2) is the (1,2) and (2,1) element, etc.
[in]	SD	SD is DOUBLE PRECISION array, dimension (N) The diagonal of the (Hermitian tri-) diagonal matrix S.
[in]	SE	SE is DOUBLE PRECISION array, dimension (N) The off-diagonal of the (Hermitian tri-) diagonal matrix S. Not referenced if KBSND=0. If KBAND=1, then AE(1) is ignored, SE(2) is the (1,2) and (2,1) element, etc.
[in]	U	U is DOUBLE PRECISION array, dimension (LDU, N) The unitary matrix in the decomposition.
[in]	LDU	LDU is INTEGER The leading dimension of U. LDU must be at least N.
[out]	WORK	WORK is COMPLEX*16 array, dimension (LDWORK, M+1)
[in]	LDWORK	LDWORK is INTEGER The leading dimension of WORK. LDWORK must be at least max(1,M).
[out]	RWORK	RWORK is DOUBLE PRECISION array, dimension (N)
[out]	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.

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.