LAPACK 3.12.1
LAPACK: Linear Algebra PACKage
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◆ drzt02()

double precision function drzt02 ( integer m,
integer n,
double precision, dimension( lda, * ) af,
integer lda,
double precision, dimension( * ) tau,
double precision, dimension( lwork ) work,
integer lwork )

DRZT02

Purpose:
!>
!> DRZT02 returns
!>      || I - Q'*Q || / ( M * eps)
!> where the matrix Q is defined by the Householder transformations
!> generated by DTZRZF.
!>
Parameters
[in]M
!>          M is INTEGER
!>          The number of rows of the matrix AF.
!>
[in]N
!>          N is INTEGER
!>          The number of columns of the matrix AF.
!>
[in]AF
!>          AF is DOUBLE PRECISION array, dimension (LDA,N)
!>          The output of DTZRZF.
!>
[in]LDA
!>          LDA is INTEGER
!>          The leading dimension of the array AF.
!>
[in]TAU
!>          TAU is DOUBLE PRECISION array, dimension (M)
!>          Details of the Householder transformations as returned by
!>          DTZRZF.
!>
[out]WORK
!>          WORK is DOUBLE PRECISION array, dimension (LWORK)
!>
[in]LWORK
!>          LWORK is INTEGER
!>          length of WORK array. LWORK >= N*N+N*NB.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 89 of file drzt02.f.

91*
92* -- LAPACK test routine --
93* -- LAPACK is a software package provided by Univ. of Tennessee, --
94* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
95*
96* .. Scalar Arguments ..
97 INTEGER LDA, LWORK, M, N
98* ..
99* .. Array Arguments ..
100 DOUBLE PRECISION AF( LDA, * ), TAU( * ), WORK( LWORK )
101* ..
102*
103* =====================================================================
104*
105* .. Parameters ..
106 DOUBLE PRECISION ZERO, ONE
107 parameter( zero = 0.0d+0, one = 1.0d+0 )
108* ..
109* .. Local Scalars ..
110 INTEGER I, INFO
111* ..
112* .. Local Arrays ..
113 DOUBLE PRECISION RWORK( 1 )
114* ..
115* .. External Functions ..
116 DOUBLE PRECISION DLAMCH, DLANGE
117 EXTERNAL dlamch, dlange
118* ..
119* .. External Subroutines ..
120 EXTERNAL dlaset, dormrz, xerbla
121* ..
122* .. Intrinsic Functions ..
123 INTRINSIC dble, max
124* ..
125* .. Executable Statements ..
126*
127 drzt02 = zero
128*
129 IF( lwork.LT.n*n+n ) THEN
130 CALL xerbla( 'DRZT02', 7 )
131 RETURN
132 END IF
133*
134* Quick return if possible
135*
136 IF( m.LE.0 .OR. n.LE.0 )
137 $ RETURN
138*
139* Q := I
140*
141 CALL dlaset( 'Full', n, n, zero, one, work, n )
142*
143* Q := P(1) * ... * P(m) * Q
144*
145 CALL dormrz( 'Left', 'No transpose', n, n, m, n-m, af, lda, tau,
146 $ work, n, work( n*n+1 ), lwork-n*n, info )
147*
148* Q := P(m) * ... * P(1) * Q
149*
150 CALL dormrz( 'Left', 'Transpose', n, n, m, n-m, af, lda, tau,
151 $ work, n, work( n*n+1 ), lwork-n*n, info )
152*
153* Q := Q - I
154*
155 DO 10 i = 1, n
156 work( ( i-1 )*n+i ) = work( ( i-1 )*n+i ) - one
157 10 CONTINUE
158*
159 drzt02 = dlange( 'One-norm', n, n, work, n, rwork ) /
160 $ ( dlamch( 'Epsilon' )*dble( max( m, n ) ) )
161 RETURN
162*
163* End of DRZT02
164*
xerbla
subroutine xerbla(srname, info)
Definition cblat2.f:3285
drzt02
double precision function drzt02(m, n, af, lda, tau, work, lwork)
DRZT02
Definition drzt02.f:91
dlamch
double precision function dlamch(cmach)
DLAMCH
Definition dlamch.f:69
dlange
double precision function dlange(norm, m, n, a, lda, work)
DLANGE returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition dlange.f:112
dlaset
subroutine dlaset(uplo, m, n, alpha, beta, a, lda)
DLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition dlaset.f:108
dormrz
subroutine dormrz(side, trans, m, n, k, l, a, lda, tau, c, ldc, work, lwork, info)
DORMRZ
Definition dormrz.f:186
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