LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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dsysv_rk.f
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1*> \brief <b> DSYSV_RK computes the solution to system of linear equations A * X = B for SY matrices</b>
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
9*> Download DSYSV_RK + dependencies
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11*> [TGZ]</a>
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13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dsysv_rk.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE DSYSV_RK( UPLO, N, NRHS, A, LDA, E, IPIV, B, LDB,
22* WORK, LWORK, INFO )
23*
24* .. Scalar Arguments ..
25* CHARACTER UPLO
26* INTEGER INFO, LDA, LDB, LWORK, N, NRHS
27* ..
28* .. Array Arguments ..
29* INTEGER IPIV( * )
30* DOUBLE PRECISION A( LDA, * ), B( LDB, * ), E( * ), WORK( * )
31* ..
32*
33*
34*> \par Purpose:
35* =============
36*>
37*> \verbatim
38*> DSYSV_RK computes the solution to a real system of linear
39*> equations A * X = B, where A is an N-by-N symmetric matrix
40*> and X and B are N-by-NRHS matrices.
41*>
42*> The bounded Bunch-Kaufman (rook) diagonal pivoting method is used
43*> to factor A as
44*> A = P*U*D*(U**T)*(P**T), if UPLO = 'U', or
45*> A = P*L*D*(L**T)*(P**T), if UPLO = 'L',
46*> where U (or L) is unit upper (or lower) triangular matrix,
47*> U**T (or L**T) is the transpose of U (or L), P is a permutation
48*> matrix, P**T is the transpose of P, and D is symmetric and block
49*> diagonal with 1-by-1 and 2-by-2 diagonal blocks.
50*>
51*> DSYTRF_RK is called to compute the factorization of a real
52*> symmetric matrix. The factored form of A is then used to solve
53*> the system of equations A * X = B by calling BLAS3 routine DSYTRS_3.
54*> \endverbatim
55*
56* Arguments:
57* ==========
58*
59*> \param[in] UPLO
60*> \verbatim
61*> UPLO is CHARACTER*1
62*> Specifies whether the upper or lower triangular part of the
63*> symmetric matrix A is stored:
64*> = 'U': Upper triangle of A is stored;
65*> = 'L': Lower triangle of A is stored.
66*> \endverbatim
67*>
68*> \param[in] N
69*> \verbatim
70*> N is INTEGER
71*> The number of linear equations, i.e., the order of the
72*> matrix A. N >= 0.
73*> \endverbatim
74*>
75*> \param[in] NRHS
76*> \verbatim
77*> NRHS is INTEGER
78*> The number of right hand sides, i.e., the number of columns
79*> of the matrix B. NRHS >= 0.
80*> \endverbatim
81*>
82*> \param[in,out] A
83*> \verbatim
84*> A is DOUBLE PRECISION array, dimension (LDA,N)
85*> On entry, the symmetric matrix A.
86*> If UPLO = 'U': the leading N-by-N upper triangular part
87*> of A contains the upper triangular part of the matrix A,
88*> and the strictly lower triangular part of A is not
89*> referenced.
90*>
91*> If UPLO = 'L': the leading N-by-N lower triangular part
92*> of A contains the lower triangular part of the matrix A,
93*> and the strictly upper triangular part of A is not
94*> referenced.
95*>
96*> On exit, if INFO = 0, diagonal of the block diagonal
97*> matrix D and factors U or L as computed by DSYTRF_RK:
98*> a) ONLY diagonal elements of the symmetric block diagonal
99*> matrix D on the diagonal of A, i.e. D(k,k) = A(k,k);
100*> (superdiagonal (or subdiagonal) elements of D
101*> are stored on exit in array E), and
102*> b) If UPLO = 'U': factor U in the superdiagonal part of A.
103*> If UPLO = 'L': factor L in the subdiagonal part of A.
104*>
105*> For more info see the description of DSYTRF_RK routine.
106*> \endverbatim
107*>
108*> \param[in] LDA
109*> \verbatim
110*> LDA is INTEGER
111*> The leading dimension of the array A. LDA >= max(1,N).
112*> \endverbatim
113*>
114*> \param[out] E
115*> \verbatim
116*> E is DOUBLE PRECISION array, dimension (N)
117*> On exit, contains the output computed by the factorization
118*> routine DSYTRF_RK, i.e. the superdiagonal (or subdiagonal)
119*> elements of the symmetric block diagonal matrix D
120*> with 1-by-1 or 2-by-2 diagonal blocks, where
121*> If UPLO = 'U': E(i) = D(i-1,i), i=2:N, E(1) is set to 0;
122*> If UPLO = 'L': E(i) = D(i+1,i), i=1:N-1, E(N) is set to 0.
123*>
124*> NOTE: For 1-by-1 diagonal block D(k), where
125*> 1 <= k <= N, the element E(k) is set to 0 in both
126*> UPLO = 'U' or UPLO = 'L' cases.
127*>
128*> For more info see the description of DSYTRF_RK routine.
129*> \endverbatim
130*>
131*> \param[out] IPIV
132*> \verbatim
133*> IPIV is INTEGER array, dimension (N)
134*> Details of the interchanges and the block structure of D,
135*> as determined by DSYTRF_RK.
136*>
137*> For more info see the description of DSYTRF_RK routine.
138*> \endverbatim
139*>
140*> \param[in,out] B
141*> \verbatim
142*> B is DOUBLE PRECISION array, dimension (LDB,NRHS)
143*> On entry, the N-by-NRHS right hand side matrix B.
144*> On exit, if INFO = 0, the N-by-NRHS solution matrix X.
145*> \endverbatim
146*>
147*> \param[in] LDB
148*> \verbatim
149*> LDB is INTEGER
150*> The leading dimension of the array B. LDB >= max(1,N).
151*> \endverbatim
152*>
153*> \param[out] WORK
154*> \verbatim
155*> WORK is DOUBLE PRECISION array, dimension ( MAX(1,LWORK) ).
156*> Work array used in the factorization stage.
157*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
158*> \endverbatim
159*>
160*> \param[in] LWORK
161*> \verbatim
162*> LWORK is INTEGER
163*> The length of WORK. LWORK >= 1. For best performance
164*> of factorization stage LWORK >= max(1,N*NB), where NB is
165*> the optimal blocksize for DSYTRF_RK.
166*>
167*> If LWORK = -1, then a workspace query is assumed;
168*> the routine only calculates the optimal size of the WORK
169*> array for factorization stage, returns this value as
170*> the first entry of the WORK array, and no error message
171*> related to LWORK is issued by XERBLA.
172*> \endverbatim
173*>
174*> \param[out] INFO
175*> \verbatim
176*> INFO is INTEGER
177*> = 0: successful exit
178*>
179*> < 0: If INFO = -k, the k-th argument had an illegal value
180*>
181*> > 0: If INFO = k, the matrix A is singular, because:
182*> If UPLO = 'U': column k in the upper
183*> triangular part of A contains all zeros.
184*> If UPLO = 'L': column k in the lower
185*> triangular part of A contains all zeros.
186*>
187*> Therefore D(k,k) is exactly zero, and superdiagonal
188*> elements of column k of U (or subdiagonal elements of
189*> column k of L ) are all zeros. The factorization has
190*> been completed, but the block diagonal matrix D is
191*> exactly singular, and division by zero will occur if
192*> it is used to solve a system of equations.
193*>
194*> NOTE: INFO only stores the first occurrence of
195*> a singularity, any subsequent occurrence of singularity
196*> is not stored in INFO even though the factorization
197*> always completes.
198*> \endverbatim
199*
200* Authors:
201* ========
202*
203*> \author Univ. of Tennessee
204*> \author Univ. of California Berkeley
205*> \author Univ. of Colorado Denver
206*> \author NAG Ltd.
207*
208*> \ingroup doubleSYsolve
209*
210*> \par Contributors:
211* ==================
212*>
213*> \verbatim
214*>
215*> December 2016, Igor Kozachenko,
216*> Computer Science Division,
217*> University of California, Berkeley
218*>
219*> September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas,
220*> School of Mathematics,
221*> University of Manchester
222*>
223*> \endverbatim
224*
225* =====================================================================
226 SUBROUTINE dsysv_rk( UPLO, N, NRHS, A, LDA, E, IPIV, B, LDB,
227 $ WORK, LWORK, INFO )
228*
229* -- LAPACK driver routine --
230* -- LAPACK is a software package provided by Univ. of Tennessee, --
231* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
232*
233* .. Scalar Arguments ..
234 CHARACTER UPLO
235 INTEGER INFO, LDA, LDB, LWORK, N, NRHS
236* ..
237* .. Array Arguments ..
238 INTEGER IPIV( * )
239 DOUBLE PRECISION A( LDA, * ), B( LDB, * ), E( * ), WORK( * )
240* ..
241*
242* =====================================================================
243*
244* .. Local Scalars ..
245 LOGICAL LQUERY
246 INTEGER LWKOPT
247* ..
248* .. External Functions ..
249 LOGICAL LSAME
250 EXTERNAL lsame
251* ..
252* .. External Subroutines ..
253 EXTERNAL xerbla, dsytrf_rk, dsytrs_3
254* ..
255* .. Intrinsic Functions ..
256 INTRINSIC max
257* ..
258* .. Executable Statements ..
259*
260* Test the input parameters.
261*
262 info = 0
263 lquery = ( lwork.EQ.-1 )
264 IF( .NOT.lsame( uplo, 'U' ) .AND. .NOT.lsame( uplo, 'L' ) ) THEN
265 info = -1
266 ELSE IF( n.LT.0 ) THEN
267 info = -2
268 ELSE IF( nrhs.LT.0 ) THEN
269 info = -3
270 ELSE IF( lda.LT.max( 1, n ) ) THEN
271 info = -5
272 ELSE IF( ldb.LT.max( 1, n ) ) THEN
273 info = -9
274 ELSE IF( lwork.LT.1 .AND. .NOT.lquery ) THEN
275 info = -11
276 END IF
277*
278 IF( info.EQ.0 ) THEN
279 IF( n.EQ.0 ) THEN
280 lwkopt = 1
281 ELSE
282 CALL dsytrf_rk( uplo, n, a, lda, e, ipiv, work, -1, info )
283 lwkopt = int( work( 1 ) )
284 END IF
285 work( 1 ) = lwkopt
286 END IF
287*
288 IF( info.NE.0 ) THEN
289 CALL xerbla( 'DSYSV_RK ', -info )
290 RETURN
291 ELSE IF( lquery ) THEN
292 RETURN
293 END IF
294*
295* Compute the factorization A = P*U*D*(U**T)*(P**T) or
296* A = P*U*D*(U**T)*(P**T).
297*
298 CALL dsytrf_rk( uplo, n, a, lda, e, ipiv, work, lwork, info )
299*
300 IF( info.EQ.0 ) THEN
301*
302* Solve the system A*X = B with BLAS3 solver, overwriting B with X.
303*
304 CALL dsytrs_3( uplo, n, nrhs, a, lda, e, ipiv, b, ldb, info )
305*
306 END IF
307*
308 work( 1 ) = lwkopt
309*
310 RETURN
311*
312* End of DSYSV_RK
313*
314 END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine dsytrf_rk(UPLO, N, A, LDA, E, IPIV, WORK, LWORK, INFO)
DSYTRF_RK computes the factorization of a real symmetric indefinite matrix using the bounded Bunch-Ka...
Definition: dsytrf_rk.f:259
subroutine dsytrs_3(UPLO, N, NRHS, A, LDA, E, IPIV, B, LDB, INFO)
DSYTRS_3
Definition: dsytrs_3.f:165
subroutine dsysv_rk(UPLO, N, NRHS, A, LDA, E, IPIV, B, LDB, WORK, LWORK, INFO)
DSYSV_RK computes the solution to system of linear equations A * X = B for SY matrices
Definition: dsysv_rk.f:228