101 SUBROUTINE clagsy( N, K, D, A, LDA, ISEED, WORK, INFO )
108 INTEGER INFO, K, LDA, N
113 COMPLEX A( LDA, * ), WORK( * )
119 COMPLEX ZERO, ONE, HALF
120 parameter( zero = ( 0.0e+0, 0.0e+0 ),
121 $ one = ( 1.0e+0, 0.0e+0 ),
122 $ half = ( 0.5e+0, 0.0e+0 ) )
127 COMPLEX ALPHA, TAU, WA, WB
136 EXTERNAL scnrm2, cdotc
139 INTRINSIC abs, max, real
148 ELSE IF( k.LT.0 .OR. k.GT.n-1 )
THEN
150 ELSE IF( lda.LT.max( 1, n ) )
THEN
154 CALL xerbla(
'CLAGSY', -info )
171 DO 60 i = n - 1, 1, -1
175 CALL clarnv( 3, iseed, n-i+1, work )
176 wn = scnrm2( n-i+1, work, 1 )
177 wa = ( wn / abs( work( 1 ) ) )*work( 1 )
178 IF( wn.EQ.zero )
THEN
182 CALL cscal( n-i, one / wb, work( 2 ), 1 )
184 tau = real( wb / wa )
192 CALL clacgv( n-i+1, work, 1 )
193 CALL csymv(
'Lower', n-i+1, tau, a( i, i ), lda, work, 1, zero,
195 CALL clacgv( n-i+1, work, 1 )
199 alpha = -half*tau*cdotc( n-i+1, work, 1, work( n+1 ), 1 )
200 CALL caxpy( n-i+1, alpha, work, 1, work( n+1 ), 1 )
209 a( ii, jj ) = a( ii, jj ) -
210 $ work( ii-i+1 )*work( n+jj-i+1 ) -
211 $ work( n+ii-i+1 )*work( jj-i+1 )
218 DO 100 i = 1, n - 1 - k
222 wn = scnrm2( n-k-i+1, a( k+i, i ), 1 )
223 wa = ( wn / abs( a( k+i, i ) ) )*a( k+i, i )
224 IF( wn.EQ.zero )
THEN
227 wb = a( k+i, i ) + wa
228 CALL cscal( n-k-i, one / wb, a( k+i+1, i ), 1 )
230 tau = real( wb / wa )
235 CALL cgemv(
'Conjugate transpose', n-k-i+1, k-1, one,
236 $ a( k+i, i+1 ), lda, a( k+i, i ), 1, zero, work, 1 )
237 CALL cgerc( n-k-i+1, k-1, -tau, a( k+i, i ), 1, work, 1,
238 $ a( k+i, i+1 ), lda )
244 CALL clacgv( n-k-i+1, a( k+i, i ), 1 )
245 CALL csymv(
'Lower', n-k-i+1, tau, a( k+i, k+i ), lda,
246 $ a( k+i, i ), 1, zero, work, 1 )
247 CALL clacgv( n-k-i+1, a( k+i, i ), 1 )
251 alpha = -half*tau*cdotc( n-k-i+1, a( k+i, i ), 1, work, 1 )
252 CALL caxpy( n-k-i+1, alpha, a( k+i, i ), 1, work, 1 )
261 a( ii, jj ) = a( ii, jj ) - a( ii, i )*work( jj-k-i+1 ) -
262 $ work( ii-k-i+1 )*a( jj, i )
267 DO 90 j = k + i + 1, n
276 a( j, i ) = a( i, j )
subroutine csymv(uplo, n, alpha, a, lda, x, incx, beta, y, incy)
CSYMV computes a matrix-vector product for a complex symmetric matrix.