LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 double precision function dla_syrcond ( character UPLO, integer N, double precision, dimension( lda, * ) A, integer LDA, double precision, dimension( ldaf, * ) AF, integer LDAF, integer, dimension( * ) IPIV, integer CMODE, double precision, dimension( * ) C, integer INFO, double precision, dimension( * ) WORK, integer, dimension( * ) IWORK )

DLA_SYRCOND estimates the Skeel condition number for a symmetric indefinite matrix.

Purpose:
```    DLA_SYRCOND estimates the Skeel condition number of  op(A) * op2(C)
where op2 is determined by CMODE as follows
CMODE =  1    op2(C) = C
CMODE =  0    op2(C) = I
CMODE = -1    op2(C) = inv(C)
The Skeel condition number cond(A) = norminf( |inv(A)||A| )
is computed by computing scaling factors R such that
diag(R)*A*op2(C) is row equilibrated and computing the standard
infinity-norm condition number.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 = 'U': Upper triangle of A is stored; = 'L': Lower triangle of A is stored.``` [in] N ``` N is INTEGER The number of linear equations, i.e., the order of the matrix A. N >= 0.``` [in] A ``` A is DOUBLE PRECISION 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 DOUBLE PRECISION array, dimension (LDAF,N) The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by DSYTRF.``` [in] LDAF ``` LDAF is INTEGER The leading dimension of the array AF. LDAF >= max(1,N).``` [in] IPIV ``` IPIV is INTEGER array, dimension (N) Details of the interchanges and the block structure of D as determined by DSYTRF.``` [in] CMODE ``` CMODE is INTEGER Determines op2(C) in the formula op(A) * op2(C) as follows: CMODE = 1 op2(C) = C CMODE = 0 op2(C) = I CMODE = -1 op2(C) = inv(C)``` [in] C ``` C is DOUBLE PRECISION array, dimension (N) The vector C in the formula op(A) * op2(C).``` [out] INFO ``` INFO is INTEGER = 0: Successful exit. i > 0: The ith argument is invalid.``` [in] WORK ``` WORK is DOUBLE PRECISION array, dimension (3*N). Workspace.``` [in] IWORK ``` IWORK is INTEGER array, dimension (N). Workspace.```
Date
September 2012

Definition at line 150 of file dla_syrcond.f.

150 *
151 * -- LAPACK computational routine (version 3.4.2) --
152 * -- LAPACK is a software package provided by Univ. of Tennessee, --
153 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
154 * September 2012
155 *
156 * .. Scalar Arguments ..
157  CHARACTER uplo
158  INTEGER n, lda, ldaf, info, cmode
159 * ..
160 * .. Array Arguments
161  INTEGER iwork( * ), ipiv( * )
162  DOUBLE PRECISION a( lda, * ), af( ldaf, * ), work( * ), c( * )
163 * ..
164 *
165 * =====================================================================
166 *
167 * .. Local Scalars ..
168  CHARACTER normin
169  INTEGER kase, i, j
170  DOUBLE PRECISION ainvnm, smlnum, tmp
171  LOGICAL up
172 * ..
173 * .. Local Arrays ..
174  INTEGER isave( 3 )
175 * ..
176 * .. External Functions ..
177  LOGICAL lsame
178  INTEGER idamax
179  DOUBLE PRECISION dlamch
180  EXTERNAL lsame, idamax, dlamch
181 * ..
182 * .. External Subroutines ..
183  EXTERNAL dlacn2, dlatrs, drscl, xerbla, dsytrs
184 * ..
185 * .. Intrinsic Functions ..
186  INTRINSIC abs, max
187 * ..
188 * .. Executable Statements ..
189 *
190  dla_syrcond = 0.0d+0
191 *
192  info = 0
193  IF( n.LT.0 ) THEN
194  info = -2
195  ELSE IF( lda.LT.max( 1, n ) ) THEN
196  info = -4
197  ELSE IF( ldaf.LT.max( 1, n ) ) THEN
198  info = -6
199  END IF
200  IF( info.NE.0 ) THEN
201  CALL xerbla( 'DLA_SYRCOND', -info )
202  RETURN
203  END IF
204  IF( n.EQ.0 ) THEN
205  dla_syrcond = 1.0d+0
206  RETURN
207  END IF
208  up = .false.
209  IF ( lsame( uplo, 'U' ) ) up = .true.
210 *
211 * Compute the equilibration matrix R such that
212 * inv(R)*A*C has unit 1-norm.
213 *
214  IF ( up ) THEN
215  DO i = 1, n
216  tmp = 0.0d+0
217  IF ( cmode .EQ. 1 ) THEN
218  DO j = 1, i
219  tmp = tmp + abs( a( j, i ) * c( j ) )
220  END DO
221  DO j = i+1, n
222  tmp = tmp + abs( a( i, j ) * c( j ) )
223  END DO
224  ELSE IF ( cmode .EQ. 0 ) THEN
225  DO j = 1, i
226  tmp = tmp + abs( a( j, i ) )
227  END DO
228  DO j = i+1, n
229  tmp = tmp + abs( a( i, j ) )
230  END DO
231  ELSE
232  DO j = 1, i
233  tmp = tmp + abs( a( j, i ) / c( j ) )
234  END DO
235  DO j = i+1, n
236  tmp = tmp + abs( a( i, j ) / c( j ) )
237  END DO
238  END IF
239  work( 2*n+i ) = tmp
240  END DO
241  ELSE
242  DO i = 1, n
243  tmp = 0.0d+0
244  IF ( cmode .EQ. 1 ) THEN
245  DO j = 1, i
246  tmp = tmp + abs( a( i, j ) * c( j ) )
247  END DO
248  DO j = i+1, n
249  tmp = tmp + abs( a( j, i ) * c( j ) )
250  END DO
251  ELSE IF ( cmode .EQ. 0 ) THEN
252  DO j = 1, i
253  tmp = tmp + abs( a( i, j ) )
254  END DO
255  DO j = i+1, n
256  tmp = tmp + abs( a( j, i ) )
257  END DO
258  ELSE
259  DO j = 1, i
260  tmp = tmp + abs( a( i, j) / c( j ) )
261  END DO
262  DO j = i+1, n
263  tmp = tmp + abs( a( j, i) / c( j ) )
264  END DO
265  END IF
266  work( 2*n+i ) = tmp
267  END DO
268  ENDIF
269 *
270 * Estimate the norm of inv(op(A)).
271 *
272  smlnum = dlamch( 'Safe minimum' )
273  ainvnm = 0.0d+0
274  normin = 'N'
275
276  kase = 0
277  10 CONTINUE
278  CALL dlacn2( n, work( n+1 ), work, iwork, ainvnm, kase, isave )
279  IF( kase.NE.0 ) THEN
280  IF( kase.EQ.2 ) THEN
281 *
282 * Multiply by R.
283 *
284  DO i = 1, n
285  work( i ) = work( i ) * work( 2*n+i )
286  END DO
287
288  IF ( up ) THEN
289  CALL dsytrs( 'U', n, 1, af, ldaf, ipiv, work, n, info )
290  ELSE
291  CALL dsytrs( 'L', n, 1, af, ldaf, ipiv, work, n, info )
292  ENDIF
293 *
294 * Multiply by inv(C).
295 *
296  IF ( cmode .EQ. 1 ) THEN
297  DO i = 1, n
298  work( i ) = work( i ) / c( i )
299  END DO
300  ELSE IF ( cmode .EQ. -1 ) THEN
301  DO i = 1, n
302  work( i ) = work( i ) * c( i )
303  END DO
304  END IF
305  ELSE
306 *
307 * Multiply by inv(C**T).
308 *
309  IF ( cmode .EQ. 1 ) THEN
310  DO i = 1, n
311  work( i ) = work( i ) / c( i )
312  END DO
313  ELSE IF ( cmode .EQ. -1 ) THEN
314  DO i = 1, n
315  work( i ) = work( i ) * c( i )
316  END DO
317  END IF
318
319  IF ( up ) THEN
320  CALL dsytrs( 'U', n, 1, af, ldaf, ipiv, work, n, info )
321  ELSE
322  CALL dsytrs( 'L', n, 1, af, ldaf, ipiv, work, n, info )
323  ENDIF
324 *
325 * Multiply by R.
326 *
327  DO i = 1, n
328  work( i ) = work( i ) * work( 2*n+i )
329  END DO
330  END IF
331 *
332  GO TO 10
333  END IF
334 *
335 * Compute the estimate of the reciprocal condition number.
336 *
337  IF( ainvnm .NE. 0.0d+0 )
338  \$ dla_syrcond = ( 1.0d+0 / ainvnm )
339 *
340  RETURN
341 *
integer function idamax(N, DX, INCX)
IDAMAX
Definition: idamax.f:53
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65
subroutine dlatrs(UPLO, TRANS, DIAG, NORMIN, N, A, LDA, X, SCALE, CNORM, INFO)
DLATRS solves a triangular system of equations with the scale factor set to prevent overflow...
Definition: dlatrs.f:240
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
double precision function dla_syrcond(UPLO, N, A, LDA, AF, LDAF, IPIV, CMODE, C, INFO, WORK, IWORK)
DLA_SYRCOND estimates the Skeel condition number for a symmetric indefinite matrix.
Definition: dla_syrcond.f:150
subroutine drscl(N, SA, SX, INCX)
DRSCL multiplies a vector by the reciprocal of a real scalar.
Definition: drscl.f:86
subroutine dsytrs(UPLO, N, NRHS, A, LDA, IPIV, B, LDB, INFO)
DSYTRS
Definition: dsytrs.f:122
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
subroutine dlacn2(N, V, X, ISGN, EST, KASE, ISAVE)
DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vec...
Definition: dlacn2.f:138

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