LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ zgecon()

subroutine zgecon ( character  NORM,
integer  N,
complex*16, dimension( lda, * )  A,
integer  LDA,
double precision  ANORM,
double precision  RCOND,
complex*16, dimension( * )  WORK,
double precision, dimension( * )  RWORK,
integer  INFO 
)

ZGECON

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Purpose:
 ZGECON estimates the reciprocal of the condition number of a general
 complex matrix A, in either the 1-norm or the infinity-norm, using
 the LU factorization computed by ZGETRF.

 An estimate is obtained for norm(inv(A)), and the reciprocal of the
 condition number is computed as
    RCOND = 1 / ( norm(A) * norm(inv(A)) ).
Parameters
[in]NORM
          NORM is CHARACTER*1
          Specifies whether the 1-norm condition number or the
          infinity-norm condition number is required:
          = '1' or 'O':  1-norm;
          = 'I':         Infinity-norm.
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in]A
          A is COMPLEX*16 array, dimension (LDA,N)
          The factors L and U from the factorization A = P*L*U
          as computed by ZGETRF.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[in]ANORM
          ANORM is DOUBLE PRECISION
          If NORM = '1' or 'O', the 1-norm of the original matrix A.
          If NORM = 'I', the infinity-norm of the original matrix A.
[out]RCOND
          RCOND is DOUBLE PRECISION
          The reciprocal of the condition number of the matrix A,
          computed as RCOND = 1/(norm(A) * norm(inv(A))).
[out]WORK
          WORK is COMPLEX*16 array, dimension (2*N)
[out]RWORK
          RWORK is DOUBLE PRECISION 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 122 of file zgecon.f.

124 *
125 * -- LAPACK computational routine --
126 * -- LAPACK is a software package provided by Univ. of Tennessee, --
127 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
128 *
129 * .. Scalar Arguments ..
130  CHARACTER NORM
131  INTEGER INFO, LDA, N
132  DOUBLE PRECISION ANORM, RCOND
133 * ..
134 * .. Array Arguments ..
135  DOUBLE PRECISION RWORK( * )
136  COMPLEX*16 A( LDA, * ), WORK( * )
137 * ..
138 *
139 * =====================================================================
140 *
141 * .. Parameters ..
142  DOUBLE PRECISION ONE, ZERO
143  parameter( one = 1.0d+0, zero = 0.0d+0 )
144 * ..
145 * .. Local Scalars ..
146  LOGICAL ONENRM
147  CHARACTER NORMIN
148  INTEGER IX, KASE, KASE1
149  DOUBLE PRECISION AINVNM, SCALE, SL, SMLNUM, SU
150  COMPLEX*16 ZDUM
151 * ..
152 * .. Local Arrays ..
153  INTEGER ISAVE( 3 )
154 * ..
155 * .. External Functions ..
156  LOGICAL LSAME
157  INTEGER IZAMAX
158  DOUBLE PRECISION DLAMCH
159  EXTERNAL lsame, izamax, dlamch
160 * ..
161 * .. External Subroutines ..
162  EXTERNAL xerbla, zdrscl, zlacn2, zlatrs
163 * ..
164 * .. Intrinsic Functions ..
165  INTRINSIC abs, dble, dimag, max
166 * ..
167 * .. Statement Functions ..
168  DOUBLE PRECISION CABS1
169 * ..
170 * .. Statement Function definitions ..
171  cabs1( zdum ) = abs( dble( zdum ) ) + abs( dimag( zdum ) )
172 * ..
173 * .. Executable Statements ..
174 *
175 * Test the input parameters.
176 *
177  info = 0
178  onenrm = norm.EQ.'1' .OR. lsame( norm, 'O' )
179  IF( .NOT.onenrm .AND. .NOT.lsame( norm, 'I' ) ) THEN
180  info = -1
181  ELSE IF( n.LT.0 ) THEN
182  info = -2
183  ELSE IF( lda.LT.max( 1, n ) ) THEN
184  info = -4
185  ELSE IF( anorm.LT.zero ) THEN
186  info = -5
187  END IF
188  IF( info.NE.0 ) THEN
189  CALL xerbla( 'ZGECON', -info )
190  RETURN
191  END IF
192 *
193 * Quick return if possible
194 *
195  rcond = zero
196  IF( n.EQ.0 ) THEN
197  rcond = one
198  RETURN
199  ELSE IF( anorm.EQ.zero ) THEN
200  RETURN
201  END IF
202 *
203  smlnum = dlamch( 'Safe minimum' )
204 *
205 * Estimate the norm of inv(A).
206 *
207  ainvnm = zero
208  normin = 'N'
209  IF( onenrm ) THEN
210  kase1 = 1
211  ELSE
212  kase1 = 2
213  END IF
214  kase = 0
215  10 CONTINUE
216  CALL zlacn2( n, work( n+1 ), work, ainvnm, kase, isave )
217  IF( kase.NE.0 ) THEN
218  IF( kase.EQ.kase1 ) THEN
219 *
220 * Multiply by inv(L).
221 *
222  CALL zlatrs( 'Lower', 'No transpose', 'Unit', normin, n, a,
223  $ lda, work, sl, rwork, info )
224 *
225 * Multiply by inv(U).
226 *
227  CALL zlatrs( 'Upper', 'No transpose', 'Non-unit', normin, n,
228  $ a, lda, work, su, rwork( n+1 ), info )
229  ELSE
230 *
231 * Multiply by inv(U**H).
232 *
233  CALL zlatrs( 'Upper', 'Conjugate transpose', 'Non-unit',
234  $ normin, n, a, lda, work, su, rwork( n+1 ),
235  $ info )
236 *
237 * Multiply by inv(L**H).
238 *
239  CALL zlatrs( 'Lower', 'Conjugate transpose', 'Unit', normin,
240  $ n, a, lda, work, sl, rwork, info )
241  END IF
242 *
243 * Divide X by 1/(SL*SU) if doing so will not cause overflow.
244 *
245  scale = sl*su
246  normin = 'Y'
247  IF( scale.NE.one ) THEN
248  ix = izamax( n, work, 1 )
249  IF( scale.LT.cabs1( work( ix ) )*smlnum .OR. scale.EQ.zero )
250  $ GO TO 20
251  CALL zdrscl( n, scale, work, 1 )
252  END IF
253  GO TO 10
254  END IF
255 *
256 * Compute the estimate of the reciprocal condition number.
257 *
258  IF( ainvnm.NE.zero )
259  $ rcond = ( one / ainvnm ) / anorm
260 *
261  20 CONTINUE
262  RETURN
263 *
264 * End of ZGECON
265 *
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69
integer function izamax(N, ZX, INCX)
IZAMAX
Definition: izamax.f:71
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine zlacn2(N, V, X, EST, KASE, ISAVE)
ZLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vec...
Definition: zlacn2.f:133
subroutine zlatrs(UPLO, TRANS, DIAG, NORMIN, N, A, LDA, X, SCALE, CNORM, INFO)
ZLATRS solves a triangular system of equations with the scale factor set to prevent overflow.
Definition: zlatrs.f:239
subroutine zdrscl(N, SA, SX, INCX)
ZDRSCL multiplies a vector by the reciprocal of a real scalar.
Definition: zdrscl.f:84
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