LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ zqrt11()

double precision function zqrt11 ( integer  M,
integer  K,
complex*16, dimension( lda, * )  A,
integer  LDA,
complex*16, dimension( * )  TAU,
complex*16, dimension( lwork )  WORK,
integer  LWORK 
)

ZQRT11

Purpose:
 ZQRT11 computes the test ratio

       || Q'*Q - I || / (eps * m)

 where the orthogonal matrix Q is represented as a product of
 elementary transformations.  Each transformation has the form

    H(k) = I - tau(k) v(k) v(k)'

 where tau(k) is stored in TAU(k) and v(k) is an m-vector of the form
 [ 0 ... 0 1 x(k) ]', where x(k) is a vector of length m-k stored
 in A(k+1:m,k).
Parameters
[in]M
          M is INTEGER
          The number of rows of the matrix A.
[in]K
          K is INTEGER
          The number of columns of A whose subdiagonal entries
          contain information about orthogonal transformations.
[in]A
          A is COMPLEX*16 array, dimension (LDA,K)
          The (possibly partial) output of a QR reduction routine.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.
[in]TAU
          TAU is COMPLEX*16 array, dimension (K)
          The scaling factors tau for the elementary transformations as
          computed by the QR factorization routine.
[out]WORK
          WORK is COMPLEX*16 array, dimension (LWORK)
[in]LWORK
          LWORK is INTEGER
          The length of the array WORK.  LWORK >= M*M + M.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 97 of file zqrt11.f.

98 *
99 * -- LAPACK test routine --
100 * -- LAPACK is a software package provided by Univ. of Tennessee, --
101 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
102 *
103 * .. Scalar Arguments ..
104  INTEGER K, LDA, LWORK, M
105 * ..
106 * .. Array Arguments ..
107  COMPLEX*16 A( LDA, * ), TAU( * ), WORK( LWORK )
108 * ..
109 *
110 * =====================================================================
111 *
112 * .. Parameters ..
113  DOUBLE PRECISION ZERO, ONE
114  parameter( zero = 0.0d0, one = 1.0d0 )
115 * ..
116 * .. Local Scalars ..
117  INTEGER INFO, J
118 * ..
119 * .. External Functions ..
120  DOUBLE PRECISION DLAMCH, ZLANGE
121  EXTERNAL dlamch, zlange
122 * ..
123 * .. External Subroutines ..
124  EXTERNAL xerbla, zlaset, zunm2r
125 * ..
126 * .. Intrinsic Functions ..
127  INTRINSIC dble, dcmplx
128 * ..
129 * .. Local Arrays ..
130  DOUBLE PRECISION RDUMMY( 1 )
131 * ..
132 * .. Executable Statements ..
133 *
134  zqrt11 = zero
135 *
136 * Test for sufficient workspace
137 *
138  IF( lwork.LT.m*m+m ) THEN
139  CALL xerbla( 'ZQRT11', 7 )
140  RETURN
141  END IF
142 *
143 * Quick return if possible
144 *
145  IF( m.LE.0 )
146  $ RETURN
147 *
148  CALL zlaset( 'Full', m, m, dcmplx( zero ), dcmplx( one ), work,
149  $ m )
150 *
151 * Form Q
152 *
153  CALL zunm2r( 'Left', 'No transpose', m, m, k, a, lda, tau, work,
154  $ m, work( m*m+1 ), info )
155 *
156 * Form Q'*Q
157 *
158  CALL zunm2r( 'Left', 'Conjugate transpose', m, m, k, a, lda, tau,
159  $ work, m, work( m*m+1 ), info )
160 *
161  DO 10 j = 1, m
162  work( ( j-1 )*m+j ) = work( ( j-1 )*m+j ) - one
163  10 CONTINUE
164 *
165  zqrt11 = zlange( 'One-norm', m, m, work, m, rdummy ) /
166  $ ( dble( m )*dlamch( 'Epsilon' ) )
167 *
168  RETURN
169 *
170 * End of ZQRT11
171 *
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
double precision function zqrt11(M, K, A, LDA, TAU, WORK, LWORK)
ZQRT11
Definition: zqrt11.f:98
double precision function zlange(NORM, M, N, A, LDA, WORK)
ZLANGE returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value ...
Definition: zlange.f:115
subroutine zlaset(UPLO, M, N, ALPHA, BETA, A, LDA)
ZLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition: zlaset.f:106
subroutine zunm2r(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, INFO)
ZUNM2R multiplies a general matrix by the unitary matrix from a QR factorization determined by cgeqrf...
Definition: zunm2r.f:159
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