LAPACK 3.11.0 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.```

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*
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69
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:110
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
double precision function drzt02(M, N, AF, LDA, TAU, WORK, LWORK)
DRZT02
Definition: drzt02.f:91
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:114
subroutine dormrz(SIDE, TRANS, M, N, K, L, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
DORMRZ
Definition: dormrz.f:187
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