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21 * SUBROUTINE DLASYF_AA( UPLO, J1, M, NB, A, LDA, IPIV,
24 * .. Scalar Arguments ..
26 * INTEGER J1, M, NB, LDA, LDH
28 * .. Array Arguments ..
30 * DOUBLE PRECISION A( LDA, * ), H( LDH, * ), WORK( * )
39 *> DLATRF_AA factorizes a panel of a real symmetric matrix A using
40 *> the Aasen's algorithm. The panel consists of a set of NB rows of A
41 *> when UPLO is U, or a set of NB columns when UPLO is L.
43 *> In order to factorize the panel, the Aasen's algorithm requires the
44 *> last row, or column, of the previous panel. The first row, or column,
45 *> of A is set to be the first row, or column, of an identity matrix,
46 *> which is used to factorize the first panel.
48 *> The resulting J-th row of U, or J-th column of L, is stored in the
49 *> (J-1)-th row, or column, of A (without the unit diagonals), while
50 *> the diagonal and subdiagonal of A are overwritten by those of T.
59 *> UPLO is CHARACTER*1
60 *> = 'U': Upper triangle of A is stored;
61 *> = 'L': Lower triangle of A is stored.
67 *> The location of the first row, or column, of the panel
68 *> within the submatrix of A, passed to this routine, e.g.,
69 *> when called by DSYTRF_AA, for the first panel, J1 is 1,
70 *> while for the remaining panels, J1 is 2.
76 *> The dimension of the submatrix. M >= 0.
82 *> The dimension of the panel to be facotorized.
87 *> A is DOUBLE PRECISION array, dimension (LDA,M) for
88 *> the first panel, while dimension (LDA,M+1) for the
91 *> On entry, A contains the last row, or column, of
92 *> the previous panel, and the trailing submatrix of A
93 *> to be factorized, except for the first panel, only
94 *> the panel is passed.
96 *> On exit, the leading panel is factorized.
102 *> The leading dimension of the array A. LDA >= max(1,M).
107 *> IPIV is INTEGER array, dimension (M)
108 *> Details of the row and column interchanges,
109 *> the row and column k were interchanged with the row and
115 *> H is DOUBLE PRECISION workspace, dimension (LDH,NB).
122 *> The leading dimension of the workspace H. LDH >= max(1,M).
127 *> WORK is DOUBLE PRECISION workspace, dimension (M).
134 *> \author Univ. of Tennessee
135 *> \author Univ. of California Berkeley
136 *> \author Univ. of Colorado Denver
139 *> \date December 2016
141 *> \ingroup doubleSYcomputational
143 * =====================================================================
144 SUBROUTINE DLASYF_AA( UPLO, J1, M, NB, A, LDA, IPIV,
147 * -- LAPACK computational routine (version 3.7.0) --
148 * -- LAPACK is a software package provided by Univ. of Tennessee, --
149 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
154 * .. Scalar Arguments ..
156 INTEGER M, NB, J1, LDA, LDH
158 * .. Array Arguments ..
160 DOUBLE PRECISION A( LDA, * ), H( LDH, * ), WORK( * )
163 * =====================================================================
165 DOUBLE PRECISION ZERO, ONE
166 PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 )
168 * .. Local Scalars ..
169 INTEGER J, K, K1, I1, I2
170 DOUBLE PRECISION PIV, ALPHA
172 * .. External Functions ..
174 INTEGER IDAMAX, ILAENV
175 EXTERNAL LSAME, ILAENV, IDAMAX
177 * .. External Subroutines ..
180 * .. Intrinsic Functions ..
183 * .. Executable Statements ..
187 * K1 is the first column of the panel to be factorized
188 * i.e., K1 is 2 for the first block column, and 1 for the rest of the blocks
192 IF( LSAME( UPLO, 'U' ) ) THEN
194 * .....................................................
195 * Factorize A as U**T*D*U using the upper triangle of A
196 * .....................................................
199 IF ( J.GT.MIN(M, NB) )
202 * K is the column to be factorized
203 * when being called from DSYTRF_AA,
204 * > for the first block column, J1 is 1, hence J1+J-1 is J,
205 * > for the rest of the columns, J1 is 2, and J1+J-1 is J+1,
209 * H(J:M, J) := A(J, J:M) - H(J:M, 1:(J-1)) * L(J1:(J-1), J),
210 * where H(J:M, J) has been initialized to be A(J, J:M)
214 * K is the column to be factorized
215 * > for the first block column, K is J, skipping the first two
217 * > for the rest of the columns, K is J+1, skipping only the
220 CALL DGEMV( 'No transpose', M-J+1, J-K1,
221 $ -ONE, H( J, K1 ), LDH,
223 $ ONE, H( J, J ), 1 )
226 * Copy H(i:M, i) into WORK
228 CALL DCOPY( M-J+1, H( J, J ), 1, WORK( 1 ), 1 )
232 * Compute WORK := WORK - L(J-1, J:M) * T(J-1,J),
233 * where A(J-1, J) stores T(J-1, J) and A(J-2, J:M) stores U(J-1, J:M)
236 CALL DAXPY( M-J+1, ALPHA, A( K-2, J ), LDA, WORK( 1 ), 1 )
239 * Set A(J, J) = T(J, J)
241 A( K, J ) = WORK( 1 )
245 * Compute WORK(2:M) = T(J, J) L(J, (J+1):M)
246 * where A(J, J) stores T(J, J) and A(J-1, (J+1):M) stores U(J, (J+1):M)
250 CALL DAXPY( M-J, ALPHA, A( K-1, J+1 ), LDA,
254 * Find max(|WORK(2:M)|)
256 I2 = IDAMAX( M-J, WORK( 2 ), 1 ) + 1
259 * Apply symmetric pivot
261 IF( (I2.NE.2) .AND. (PIV.NE.0) ) THEN
263 * Swap WORK(I1) and WORK(I2)
266 WORK( I2 ) = WORK( I1 )
269 * Swap A(I1, I1+1:M) with A(I1+1:M, I2)
273 CALL DSWAP( I2-I1-1, A( J1+I1-1, I1+1 ), LDA,
274 $ A( J1+I1, I2 ), 1 )
276 * Swap A(I1, I2+1:M) with A(I2, I2+1:M)
278 CALL DSWAP( M-I2, A( J1+I1-1, I2+1 ), LDA,
279 $ A( J1+I2-1, I2+1 ), LDA )
281 * Swap A(I1, I1) with A(I2,I2)
283 PIV = A( I1+J1-1, I1 )
284 A( J1+I1-1, I1 ) = A( J1+I2-1, I2 )
285 A( J1+I2-1, I2 ) = PIV
287 * Swap H(I1, 1:J1) with H(I2, 1:J1)
289 CALL DSWAP( I1-1, H( I1, 1 ), LDH, H( I2, 1 ), LDH )
292 IF( I1.GT.(K1-1) ) THEN
294 * Swap L(1:I1-1, I1) with L(1:I1-1, I2),
295 * skipping the first column
297 CALL DSWAP( I1-K1+1, A( 1, I1 ), 1,
304 * Set A(J, J+1) = T(J, J+1)
306 A( K, J+1 ) = WORK( 2 )
310 * Copy A(J+1:M, J+1) into H(J:M, J),
312 CALL DCOPY( M-J, A( K+1, J+1 ), LDA,
316 * Compute L(J+2, J+1) = WORK( 3:M ) / T(J, J+1),
317 * where A(J, J+1) = T(J, J+1) and A(J+2:M, J) = L(J+2:M, J+1)
319 IF( A( K, J+1 ).NE.ZERO ) THEN
320 ALPHA = ONE / A( K, J+1 )
321 CALL DCOPY( M-J-1, WORK( 3 ), 1, A( K, J+2 ), LDA )
322 CALL DSCAL( M-J-1, ALPHA, A( K, J+2 ), LDA )
324 CALL DLASET( 'Full', 1, M-J-1, ZERO, ZERO,
334 * .....................................................
335 * Factorize A as L*D*L**T using the lower triangle of A
336 * .....................................................
339 IF( J.GT.MIN( M, NB ) )
342 * K is the column to be factorized
343 * when being called from DSYTRF_AA,
344 * > for the first block column, J1 is 1, hence J1+J-1 is J,
345 * > for the rest of the columns, J1 is 2, and J1+J-1 is J+1,
349 * H(J:M, J) := A(J:M, J) - H(J:M, 1:(J-1)) * L(J, J1:(J-1))^T,
350 * where H(J:M, J) has been initialized to be A(J:M, J)
354 * K is the column to be factorized
355 * > for the first block column, K is J, skipping the first two
357 * > for the rest of the columns, K is J+1, skipping only the
360 CALL DGEMV( 'No transpose', M-J+1, J-K1,
361 $ -ONE, H( J, K1 ), LDH,
363 $ ONE, H( J, J ), 1 )
366 * Copy H(J:M, J) into WORK
368 CALL DCOPY( M-J+1, H( J, J ), 1, WORK( 1 ), 1 )
372 * Compute WORK := WORK - L(J:M, J-1) * T(J-1,J),
373 * where A(J-1, J) = T(J-1, J) and A(J, J-2) = L(J, J-1)
376 CALL DAXPY( M-J+1, ALPHA, A( J, K-2 ), 1, WORK( 1 ), 1 )
379 * Set A(J, J) = T(J, J)
381 A( J, K ) = WORK( 1 )
385 * Compute WORK(2:M) = T(J, J) L((J+1):M, J)
386 * where A(J, J) = T(J, J) and A((J+1):M, J-1) = L((J+1):M, J)
390 CALL DAXPY( M-J, ALPHA, A( J+1, K-1 ), 1,
394 * Find max(|WORK(2:M)|)
396 I2 = IDAMAX( M-J, WORK( 2 ), 1 ) + 1
399 * Apply symmetric pivot
401 IF( (I2.NE.2) .AND. (PIV.NE.0) ) THEN
403 * Swap WORK(I1) and WORK(I2)
406 WORK( I2 ) = WORK( I1 )
409 * Swap A(I1+1:M, I1) with A(I2, I1+1:M)
413 CALL DSWAP( I2-I1-1, A( I1+1, J1+I1-1 ), 1,
414 $ A( I2, J1+I1 ), LDA )
416 * Swap A(I2+1:M, I1) with A(I2+1:M, I2)
418 CALL DSWAP( M-I2, A( I2+1, J1+I1-1 ), 1,
419 $ A( I2+1, J1+I2-1 ), 1 )
421 * Swap A(I1, I1) with A(I2, I2)
423 PIV = A( I1, J1+I1-1 )
424 A( I1, J1+I1-1 ) = A( I2, J1+I2-1 )
425 A( I2, J1+I2-1 ) = PIV
427 * Swap H(I1, I1:J1) with H(I2, I2:J1)
429 CALL DSWAP( I1-1, H( I1, 1 ), LDH, H( I2, 1 ), LDH )
432 IF( I1.GT.(K1-1) ) THEN
434 * Swap L(1:I1-1, I1) with L(1:I1-1, I2),
435 * skipping the first column
437 CALL DSWAP( I1-K1+1, A( I1, 1 ), LDA,
444 * Set A(J+1, J) = T(J+1, J)
446 A( J+1, K ) = WORK( 2 )
450 * Copy A(J+1:M, J+1) into H(J+1:M, J),
452 CALL DCOPY( M-J, A( J+1, K+1 ), 1,
456 * Compute L(J+2, J+1) = WORK( 3:M ) / T(J, J+1),
457 * where A(J, J+1) = T(J, J+1) and A(J+2:M, J) = L(J+2:M, J+1)
459 IF( A( J+1, K ).NE.ZERO ) THEN
460 ALPHA = ONE / A( J+1, K )
461 CALL DCOPY( M-J-1, WORK( 3 ), 1, A( J+2, K ), 1 )
462 CALL DSCAL( M-J-1, ALPHA, A( J+2, K ), 1 )
464 CALL DLASET( 'Full', M-J-1, 1, ZERO, ZERO,