LAPACK  3.10.1
LAPACK: Linear Algebra PACKage
ssycon_3.f
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1 *> \brief \b SSYCON_3
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
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17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE SSYCON_3( UPLO, N, A, LDA, E, IPIV, ANORM, RCOND,
22 * WORK, IWORK, INFO )
23 *
24 * .. Scalar Arguments ..
25 * CHARACTER UPLO
26 * INTEGER INFO, LDA, N
27 * REAL ANORM, RCOND
28 * ..
29 * .. Array Arguments ..
30 * INTEGER IPIV( * ), IWORK( * )
31 * REAL A( LDA, * ), E ( * ), WORK( * )
32 * ..
33 *
34 *
35 *> \par Purpose:
36 * =============
37 *>
38 *> \verbatim
39 *> SSYCON_3 estimates the reciprocal of the condition number (in the
40 *> 1-norm) of a real symmetric matrix A using the factorization
41 *> computed by DSYTRF_RK or DSYTRF_BK:
42 *>
43 *> A = P*U*D*(U**T)*(P**T) or A = P*L*D*(L**T)*(P**T),
44 *>
45 *> where U (or L) is unit upper (or lower) triangular matrix,
46 *> U**T (or L**T) is the transpose of U (or L), P is a permutation
47 *> matrix, P**T is the transpose of P, and D is symmetric and block
48 *> diagonal with 1-by-1 and 2-by-2 diagonal blocks.
49 *>
50 *> An estimate is obtained for norm(inv(A)), and the reciprocal of the
51 *> condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
52 *> This routine uses BLAS3 solver SSYTRS_3.
53 *> \endverbatim
54 *
55 * Arguments:
56 * ==========
57 *
58 *> \param[in] UPLO
59 *> \verbatim
60 *> UPLO is CHARACTER*1
61 *> Specifies whether the details of the factorization are
62 *> stored as an upper or lower triangular matrix:
63 *> = 'U': Upper triangular, form is A = P*U*D*(U**T)*(P**T);
64 *> = 'L': Lower triangular, form is A = P*L*D*(L**T)*(P**T).
65 *> \endverbatim
66 *>
67 *> \param[in] N
68 *> \verbatim
69 *> N is INTEGER
70 *> The order of the matrix A. N >= 0.
71 *> \endverbatim
72 *>
73 *> \param[in] A
74 *> \verbatim
75 *> A is REAL array, dimension (LDA,N)
76 *> Diagonal of the block diagonal matrix D and factors U or L
77 *> as computed by SSYTRF_RK and SSYTRF_BK:
78 *> a) ONLY diagonal elements of the symmetric block diagonal
79 *> matrix D on the diagonal of A, i.e. D(k,k) = A(k,k);
80 *> (superdiagonal (or subdiagonal) elements of D
81 *> should be provided on entry in array E), and
82 *> b) If UPLO = 'U': factor U in the superdiagonal part of A.
83 *> If UPLO = 'L': factor L in the subdiagonal part of A.
84 *> \endverbatim
85 *>
86 *> \param[in] LDA
87 *> \verbatim
88 *> LDA is INTEGER
89 *> The leading dimension of the array A. LDA >= max(1,N).
90 *> \endverbatim
91 *>
92 *> \param[in] E
93 *> \verbatim
94 *> E is REAL array, dimension (N)
95 *> On entry, contains the superdiagonal (or subdiagonal)
96 *> elements of the symmetric block diagonal matrix D
97 *> with 1-by-1 or 2-by-2 diagonal blocks, where
98 *> If UPLO = 'U': E(i) = D(i-1,i),i=2:N, E(1) not referenced;
99 *> If UPLO = 'L': E(i) = D(i+1,i),i=1:N-1, E(N) not referenced.
100 *>
101 *> NOTE: For 1-by-1 diagonal block D(k), where
102 *> 1 <= k <= N, the element E(k) is not referenced in both
103 *> UPLO = 'U' or UPLO = 'L' cases.
104 *> \endverbatim
105 *>
106 *> \param[in] IPIV
107 *> \verbatim
108 *> IPIV is INTEGER array, dimension (N)
109 *> Details of the interchanges and the block structure of D
110 *> as determined by SSYTRF_RK or SSYTRF_BK.
111 *> \endverbatim
112 *>
113 *> \param[in] ANORM
114 *> \verbatim
115 *> ANORM is REAL
116 *> The 1-norm of the original matrix A.
117 *> \endverbatim
118 *>
119 *> \param[out] RCOND
120 *> \verbatim
121 *> RCOND is REAL
122 *> The reciprocal of the condition number of the matrix A,
123 *> computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an
124 *> estimate of the 1-norm of inv(A) computed in this routine.
125 *> \endverbatim
126 *>
127 *> \param[out] WORK
128 *> \verbatim
129 *> WORK is REAL array, dimension (2*N)
130 *> \endverbatim
131 *>
132 *> \param[out] IWORK
133 *> \verbatim
134 *> IWORK is INTEGER array, dimension (N)
135 *> \endverbatim
136 *>
137 *> \param[out] INFO
138 *> \verbatim
139 *> INFO is INTEGER
140 *> = 0: successful exit
141 *> < 0: if INFO = -i, the i-th argument had an illegal value
142 *> \endverbatim
143 *
144 * Authors:
145 * ========
146 *
147 *> \author Univ. of Tennessee
148 *> \author Univ. of California Berkeley
149 *> \author Univ. of Colorado Denver
150 *> \author NAG Ltd.
151 *
152 *> \ingroup singleSYcomputational
153 *
154 *> \par Contributors:
155 * ==================
156 *> \verbatim
157 *>
158 *> June 2017, Igor Kozachenko,
159 *> Computer Science Division,
160 *> University of California, Berkeley
161 *>
162 *> September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
163 *> School of Mathematics,
164 *> University of Manchester
165 *>
166 *> \endverbatim
167 *
168 * =====================================================================
169  SUBROUTINE ssycon_3( UPLO, N, A, LDA, E, IPIV, ANORM, RCOND,
170  $ WORK, IWORK, INFO )
171 *
172 * -- LAPACK computational routine --
173 * -- LAPACK is a software package provided by Univ. of Tennessee, --
174 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
175 *
176 * .. Scalar Arguments ..
177  CHARACTER UPLO
178  INTEGER INFO, LDA, N
179  REAL ANORM, RCOND
180 * ..
181 * .. Array Arguments ..
182  INTEGER IPIV( * ), IWORK( * )
183  REAL A( LDA, * ), E( * ), WORK( * )
184 * ..
185 *
186 * =====================================================================
187 *
188 * .. Parameters ..
189  REAL ONE, ZERO
190  parameter( one = 1.0e+0, zero = 0.0e+0 )
191 * ..
192 * .. Local Scalars ..
193  LOGICAL UPPER
194  INTEGER I, KASE
195  REAL AINVNM
196 * ..
197 * .. Local Arrays ..
198  INTEGER ISAVE( 3 )
199 * ..
200 * .. External Functions ..
201  LOGICAL LSAME
202  EXTERNAL lsame
203 * ..
204 * .. External Subroutines ..
205  EXTERNAL slacn2, ssytrs_3, xerbla
206 * ..
207 * .. Intrinsic Functions ..
208  INTRINSIC max
209 * ..
210 * .. Executable Statements ..
211 *
212 * Test the input parameters.
213 *
214  info = 0
215  upper = lsame( uplo, 'U' )
216  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
217  info = -1
218  ELSE IF( n.LT.0 ) THEN
219  info = -2
220  ELSE IF( lda.LT.max( 1, n ) ) THEN
221  info = -4
222  ELSE IF( anorm.LT.zero ) THEN
223  info = -7
224  END IF
225  IF( info.NE.0 ) THEN
226  CALL xerbla( 'SSYCON_3', -info )
227  RETURN
228  END IF
229 *
230 * Quick return if possible
231 *
232  rcond = zero
233  IF( n.EQ.0 ) THEN
234  rcond = one
235  RETURN
236  ELSE IF( anorm.LE.zero ) THEN
237  RETURN
238  END IF
239 *
240 * Check that the diagonal matrix D is nonsingular.
241 *
242  IF( upper ) THEN
243 *
244 * Upper triangular storage: examine D from bottom to top
245 *
246  DO i = n, 1, -1
247  IF( ipiv( i ).GT.0 .AND. a( i, i ).EQ.zero )
248  $ RETURN
249  END DO
250  ELSE
251 *
252 * Lower triangular storage: examine D from top to bottom.
253 *
254  DO i = 1, n
255  IF( ipiv( i ).GT.0 .AND. a( i, i ).EQ.zero )
256  $ RETURN
257  END DO
258  END IF
259 *
260 * Estimate the 1-norm of the inverse.
261 *
262  kase = 0
263  30 CONTINUE
264  CALL slacn2( n, work( n+1 ), work, iwork, ainvnm, kase, isave )
265  IF( kase.NE.0 ) THEN
266 *
267 * Multiply by inv(L*D*L**T) or inv(U*D*U**T).
268 *
269  CALL ssytrs_3( uplo, n, 1, a, lda, e, ipiv, work, n, info )
270  GO TO 30
271  END IF
272 *
273 * Compute the estimate of the reciprocal condition number.
274 *
275  IF( ainvnm.NE.zero )
276  $ rcond = ( one / ainvnm ) / anorm
277 *
278  RETURN
279 *
280 * End of SSYCON_3
281 *
282  END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine slacn2(N, V, X, ISGN, EST, KASE, ISAVE)
SLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vec...
Definition: slacn2.f:136
subroutine ssycon_3(UPLO, N, A, LDA, E, IPIV, ANORM, RCOND, WORK, IWORK, INFO)
SSYCON_3
Definition: ssycon_3.f:171
subroutine ssytrs_3(UPLO, N, NRHS, A, LDA, E, IPIV, B, LDB, INFO)
SSYTRS_3
Definition: ssytrs_3.f:165