LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ zlarge()

subroutine zlarge ( integer  N,
complex*16, dimension( lda, * )  A,
integer  LDA,
integer, dimension( 4 )  ISEED,
complex*16, dimension( * )  WORK,
integer  INFO 
)

ZLARGE

Purpose:
 ZLARGE pre- and post-multiplies a complex general n by n matrix A
 with a random unitary matrix: A = U*D*U'.
Parameters
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in,out]A
          A is COMPLEX*16 array, dimension (LDA,N)
          On entry, the original n by n matrix A.
          On exit, A is overwritten by U*A*U' for some random
          unitary matrix U.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= N.
[in,out]ISEED
          ISEED is INTEGER array, dimension (4)
          On entry, the seed of the random number generator; the array
          elements must be between 0 and 4095, and ISEED(4) must be
          odd.
          On exit, the seed is updated.
[out]WORK
          WORK is COMPLEX*16 array, dimension (2*N)
[out]INFO
          INFO is INTEGER
          = 0: successful exit
          < 0: if INFO = -i, the i-th argument had an illegal value
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 86 of file zlarge.f.

87 *
88 * -- LAPACK auxiliary routine --
89 * -- LAPACK is a software package provided by Univ. of Tennessee, --
90 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
91 *
92 * .. Scalar Arguments ..
93  INTEGER INFO, LDA, N
94 * ..
95 * .. Array Arguments ..
96  INTEGER ISEED( 4 )
97  COMPLEX*16 A( LDA, * ), WORK( * )
98 * ..
99 *
100 * =====================================================================
101 *
102 * .. Parameters ..
103  COMPLEX*16 ZERO, ONE
104  parameter( zero = ( 0.0d+0, 0.0d+0 ),
105  $ one = ( 1.0d+0, 0.0d+0 ) )
106 * ..
107 * .. Local Scalars ..
108  INTEGER I
109  DOUBLE PRECISION WN
110  COMPLEX*16 TAU, WA, WB
111 * ..
112 * .. External Subroutines ..
113  EXTERNAL xerbla, zgemv, zgerc, zlarnv, zscal
114 * ..
115 * .. Intrinsic Functions ..
116  INTRINSIC abs, dble, max
117 * ..
118 * .. External Functions ..
119  DOUBLE PRECISION DZNRM2
120  EXTERNAL dznrm2
121 * ..
122 * .. Executable Statements ..
123 *
124 * Test the input arguments
125 *
126  info = 0
127  IF( n.LT.0 ) THEN
128  info = -1
129  ELSE IF( lda.LT.max( 1, n ) ) THEN
130  info = -3
131  END IF
132  IF( info.LT.0 ) THEN
133  CALL xerbla( 'ZLARGE', -info )
134  RETURN
135  END IF
136 *
137 * pre- and post-multiply A by random unitary matrix
138 *
139  DO 10 i = n, 1, -1
140 *
141 * generate random reflection
142 *
143  CALL zlarnv( 3, iseed, n-i+1, work )
144  wn = dznrm2( n-i+1, work, 1 )
145  wa = ( wn / abs( work( 1 ) ) )*work( 1 )
146  IF( wn.EQ.zero ) THEN
147  tau = zero
148  ELSE
149  wb = work( 1 ) + wa
150  CALL zscal( n-i, one / wb, work( 2 ), 1 )
151  work( 1 ) = one
152  tau = dble( wb / wa )
153  END IF
154 *
155 * multiply A(i:n,1:n) by random reflection from the left
156 *
157  CALL zgemv( 'Conjugate transpose', n-i+1, n, one, a( i, 1 ),
158  $ lda, work, 1, zero, work( n+1 ), 1 )
159  CALL zgerc( n-i+1, n, -tau, work, 1, work( n+1 ), 1, a( i, 1 ),
160  $ lda )
161 *
162 * multiply A(1:n,i:n) by random reflection from the right
163 *
164  CALL zgemv( 'No transpose', n, n-i+1, one, a( 1, i ), lda,
165  $ work, 1, zero, work( n+1 ), 1 )
166  CALL zgerc( n, n-i+1, -tau, work( n+1 ), 1, work, 1, a( 1, i ),
167  $ lda )
168  10 CONTINUE
169  RETURN
170 *
171 * End of ZLARGE
172 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine zscal(N, ZA, ZX, INCX)
ZSCAL
Definition: zscal.f:78
subroutine zgerc(M, N, ALPHA, X, INCX, Y, INCY, A, LDA)
ZGERC
Definition: zgerc.f:130
subroutine zgemv(TRANS, M, N, ALPHA, A, LDA, X, INCX, BETA, Y, INCY)
ZGEMV
Definition: zgemv.f:158
subroutine zlarnv(IDIST, ISEED, N, X)
ZLARNV returns a vector of random numbers from a uniform or normal distribution.
Definition: zlarnv.f:99
real(wp) function dznrm2(n, x, incx)
DZNRM2
Definition: dznrm2.f90:90
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