 LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ zla_gercond_x()

 double precision function zla_gercond_x ( character TRANS, integer N, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( ldaf, * ) AF, integer LDAF, integer, dimension( * ) IPIV, complex*16, dimension( * ) X, integer INFO, complex*16, dimension( * ) WORK, double precision, dimension( * ) RWORK )

ZLA_GERCOND_X computes the infinity norm condition number of op(A)*diag(x) for general matrices.

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Purpose:
```    ZLA_GERCOND_X computes the infinity norm condition number of
op(A) * diag(X) where X is a COMPLEX*16 vector.```
Parameters
 [in] TRANS ``` TRANS is CHARACTER*1 Specifies the form of the system of equations: = 'N': A * X = B (No transpose) = 'T': A**T * X = B (Transpose) = 'C': A**H * X = B (Conjugate Transpose = Transpose)``` [in] N ``` N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.``` [in] A ``` A is COMPLEX*16 array, dimension (LDA,N) On entry, the N-by-N matrix A.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in] AF ``` AF is COMPLEX*16 array, dimension (LDAF,N) The factors L and U from the factorization A = P*L*U as computed by ZGETRF.``` [in] LDAF ``` LDAF is INTEGER The leading dimension of the array AF. LDAF >= max(1,N).``` [in] IPIV ``` IPIV is INTEGER array, dimension (N) The pivot indices from the factorization A = P*L*U as computed by ZGETRF; row i of the matrix was interchanged with row IPIV(i).``` [in] X ``` X is COMPLEX*16 array, dimension (N) The vector X in the formula op(A) * diag(X).``` [out] INFO ``` INFO is INTEGER = 0: Successful exit. i > 0: The ith argument is invalid.``` [out] WORK ``` WORK is COMPLEX*16 array, dimension (2*N). Workspace.``` [out] RWORK ``` RWORK is DOUBLE PRECISION array, dimension (N). Workspace.```

Definition at line 133 of file zla_gercond_x.f.

136 *
137 * -- LAPACK computational routine --
138 * -- LAPACK is a software package provided by Univ. of Tennessee, --
139 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
140 *
141 * .. Scalar Arguments ..
142  CHARACTER TRANS
143  INTEGER N, LDA, LDAF, INFO
144 * ..
145 * .. Array Arguments ..
146  INTEGER IPIV( * )
147  COMPLEX*16 A( LDA, * ), AF( LDAF, * ), WORK( * ), X( * )
148  DOUBLE PRECISION RWORK( * )
149 * ..
150 *
151 * =====================================================================
152 *
153 * .. Local Scalars ..
154  LOGICAL NOTRANS
155  INTEGER KASE
156  DOUBLE PRECISION AINVNM, ANORM, TMP
157  INTEGER I, J
158  COMPLEX*16 ZDUM
159 * ..
160 * .. Local Arrays ..
161  INTEGER ISAVE( 3 )
162 * ..
163 * .. External Functions ..
164  LOGICAL LSAME
165  EXTERNAL lsame
166 * ..
167 * .. External Subroutines ..
168  EXTERNAL zlacn2, zgetrs, xerbla
169 * ..
170 * .. Intrinsic Functions ..
171  INTRINSIC abs, max, real, dimag
172 * ..
173 * .. Statement Functions ..
174  DOUBLE PRECISION CABS1
175 * ..
176 * .. Statement Function Definitions ..
177  cabs1( zdum ) = abs( dble( zdum ) ) + abs( dimag( zdum ) )
178 * ..
179 * .. Executable Statements ..
180 *
181  zla_gercond_x = 0.0d+0
182 *
183  info = 0
184  notrans = lsame( trans, 'N' )
185  IF ( .NOT. notrans .AND. .NOT. lsame( trans, 'T' ) .AND. .NOT.
186  \$ lsame( trans, 'C' ) ) THEN
187  info = -1
188  ELSE IF( n.LT.0 ) THEN
189  info = -2
190  ELSE IF( lda.LT.max( 1, n ) ) THEN
191  info = -4
192  ELSE IF( ldaf.LT.max( 1, n ) ) THEN
193  info = -6
194  END IF
195  IF( info.NE.0 ) THEN
196  CALL xerbla( 'ZLA_GERCOND_X', -info )
197  RETURN
198  END IF
199 *
200 * Compute norm of op(A)*op2(C).
201 *
202  anorm = 0.0d+0
203  IF ( notrans ) THEN
204  DO i = 1, n
205  tmp = 0.0d+0
206  DO j = 1, n
207  tmp = tmp + cabs1( a( i, j ) * x( j ) )
208  END DO
209  rwork( i ) = tmp
210  anorm = max( anorm, tmp )
211  END DO
212  ELSE
213  DO i = 1, n
214  tmp = 0.0d+0
215  DO j = 1, n
216  tmp = tmp + cabs1( a( j, i ) * x( j ) )
217  END DO
218  rwork( i ) = tmp
219  anorm = max( anorm, tmp )
220  END DO
221  END IF
222 *
223 * Quick return if possible.
224 *
225  IF( n.EQ.0 ) THEN
226  zla_gercond_x = 1.0d+0
227  RETURN
228  ELSE IF( anorm .EQ. 0.0d+0 ) THEN
229  RETURN
230  END IF
231 *
232 * Estimate the norm of inv(op(A)).
233 *
234  ainvnm = 0.0d+0
235 *
236  kase = 0
237  10 CONTINUE
238  CALL zlacn2( n, work( n+1 ), work, ainvnm, kase, isave )
239  IF( kase.NE.0 ) THEN
240  IF( kase.EQ.2 ) THEN
241 * Multiply by R.
242  DO i = 1, n
243  work( i ) = work( i ) * rwork( i )
244  END DO
245 *
246  IF ( notrans ) THEN
247  CALL zgetrs( 'No transpose', n, 1, af, ldaf, ipiv,
248  \$ work, n, info )
249  ELSE
250  CALL zgetrs( 'Conjugate transpose', n, 1, af, ldaf, ipiv,
251  \$ work, n, info )
252  ENDIF
253 *
254 * Multiply by inv(X).
255 *
256  DO i = 1, n
257  work( i ) = work( i ) / x( i )
258  END DO
259  ELSE
260 *
261 * Multiply by inv(X**H).
262 *
263  DO i = 1, n
264  work( i ) = work( i ) / x( i )
265  END DO
266 *
267  IF ( notrans ) THEN
268  CALL zgetrs( 'Conjugate transpose', n, 1, af, ldaf, ipiv,
269  \$ work, n, info )
270  ELSE
271  CALL zgetrs( 'No transpose', n, 1, af, ldaf, ipiv,
272  \$ work, n, info )
273  END IF
274 *
275 * Multiply by R.
276 *
277  DO i = 1, n
278  work( i ) = work( i ) * rwork( i )
279  END DO
280  END IF
281  GO TO 10
282  END IF
283 *
284 * Compute the estimate of the reciprocal condition number.
285 *
286  IF( ainvnm .NE. 0.0d+0 )
287  \$ zla_gercond_x = 1.0d+0 / ainvnm
288 *
289  RETURN
290 *
291 * End of ZLA_GERCOND_X
292 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine zgetrs(TRANS, N, NRHS, A, LDA, IPIV, B, LDB, INFO)
ZGETRS
Definition: zgetrs.f:121
double precision function zla_gercond_x(TRANS, N, A, LDA, AF, LDAF, IPIV, X, INFO, WORK, RWORK)
ZLA_GERCOND_X computes the infinity norm condition number of op(A)*diag(x) for general matrices.
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
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