LAPACK  3.9.0
LAPACK: Linear Algebra PACKage

◆ ssyconv()

subroutine ssyconv ( character  UPLO,
character  WAY,
integer  N,
real, dimension( lda, * )  A,
integer  LDA,
integer, dimension( * )  IPIV,
real, dimension( * )  E,
integer  INFO 
)

SSYCONV

Download SSYCONV + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SSYCONV convert A given by TRF into L and D and vice-versa.
 Get Non-diag elements of D (returned in workspace) and
 apply or reverse permutation done in TRF.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          Specifies whether the details of the factorization are stored
          as an upper or lower triangular matrix.
          = 'U':  Upper triangular, form is A = U*D*U**T;
          = 'L':  Lower triangular, form is A = L*D*L**T.
[in]WAY
          WAY is CHARACTER*1
          = 'C': Convert
          = 'R': Revert
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in,out]A
          A is REAL array, dimension (LDA,N)
          The block diagonal matrix D and the multipliers used to
          obtain the factor U or L as computed by SSYTRF.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[in]IPIV
          IPIV is INTEGER array, dimension (N)
          Details of the interchanges and the block structure of D
          as determined by SSYTRF.
[out]E
          E is REAL array, dimension (N)
          E stores the supdiagonal/subdiagonal of the symmetric 1-by-1
          or 2-by-2 block diagonal matrix D in LDLT.
[out]INFO
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
December 2016

Definition at line 116 of file ssyconv.f.

116 *
117 * -- LAPACK computational routine (version 3.7.0) --
118 * -- LAPACK is a software package provided by Univ. of Tennessee, --
119 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120 * December 2016
121 *
122 * .. Scalar Arguments ..
123  CHARACTER UPLO, WAY
124  INTEGER INFO, LDA, N
125 * ..
126 * .. Array Arguments ..
127  INTEGER IPIV( * )
128  REAL A( LDA, * ), E( * )
129 * ..
130 *
131 * =====================================================================
132 *
133 * .. Parameters ..
134  REAL ZERO
135  parameter( zero = 0.0e+0 )
136 * ..
137 * .. External Functions ..
138  LOGICAL LSAME
139  EXTERNAL lsame
140 *
141 * .. External Subroutines ..
142  EXTERNAL xerbla
143 * .. Local Scalars ..
144  LOGICAL UPPER, CONVERT
145  INTEGER I, IP, J
146  REAL TEMP
147 * ..
148 * .. Executable Statements ..
149 *
150  info = 0
151  upper = lsame( uplo, 'U' )
152  convert = lsame( way, 'C' )
153  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
154  info = -1
155  ELSE IF( .NOT.convert .AND. .NOT.lsame( way, 'R' ) ) THEN
156  info = -2
157  ELSE IF( n.LT.0 ) THEN
158  info = -3
159  ELSE IF( lda.LT.max( 1, n ) ) THEN
160  info = -5
161 
162  END IF
163  IF( info.NE.0 ) THEN
164  CALL xerbla( 'SSYCONV', -info )
165  RETURN
166  END IF
167 *
168 * Quick return if possible
169 *
170  IF( n.EQ.0 )
171  $ RETURN
172 *
173  IF( upper ) THEN
174 *
175 * A is UPPER
176 *
177 * Convert A (A is upper)
178 *
179 * Convert VALUE
180 *
181  IF ( convert ) THEN
182  i=n
183  e(1)=zero
184  DO WHILE ( i .GT. 1 )
185  IF( ipiv(i) .LT. 0 ) THEN
186  e(i)=a(i-1,i)
187  e(i-1)=zero
188  a(i-1,i)=zero
189  i=i-1
190  ELSE
191  e(i)=zero
192  ENDIF
193  i=i-1
194  END DO
195 *
196 * Convert PERMUTATIONS
197 *
198  i=n
199  DO WHILE ( i .GE. 1 )
200  IF( ipiv(i) .GT. 0) THEN
201  ip=ipiv(i)
202  IF( i .LT. n) THEN
203  DO 12 j= i+1,n
204  temp=a(ip,j)
205  a(ip,j)=a(i,j)
206  a(i,j)=temp
207  12 CONTINUE
208  ENDIF
209  ELSE
210  ip=-ipiv(i)
211  IF( i .LT. n) THEN
212  DO 13 j= i+1,n
213  temp=a(ip,j)
214  a(ip,j)=a(i-1,j)
215  a(i-1,j)=temp
216  13 CONTINUE
217  ENDIF
218  i=i-1
219  ENDIF
220  i=i-1
221  END DO
222 
223  ELSE
224 *
225 * Revert A (A is upper)
226 *
227 *
228 * Revert PERMUTATIONS
229 *
230  i=1
231  DO WHILE ( i .LE. n )
232  IF( ipiv(i) .GT. 0 ) THEN
233  ip=ipiv(i)
234  IF( i .LT. n) THEN
235  DO j= i+1,n
236  temp=a(ip,j)
237  a(ip,j)=a(i,j)
238  a(i,j)=temp
239  END DO
240  ENDIF
241  ELSE
242  ip=-ipiv(i)
243  i=i+1
244  IF( i .LT. n) THEN
245  DO j= i+1,n
246  temp=a(ip,j)
247  a(ip,j)=a(i-1,j)
248  a(i-1,j)=temp
249  END DO
250  ENDIF
251  ENDIF
252  i=i+1
253  END DO
254 *
255 * Revert VALUE
256 *
257  i=n
258  DO WHILE ( i .GT. 1 )
259  IF( ipiv(i) .LT. 0 ) THEN
260  a(i-1,i)=e(i)
261  i=i-1
262  ENDIF
263  i=i-1
264  END DO
265  END IF
266  ELSE
267 *
268 * A is LOWER
269 *
270  IF ( convert ) THEN
271 *
272 * Convert A (A is lower)
273 *
274 *
275 * Convert VALUE
276 *
277  i=1
278  e(n)=zero
279  DO WHILE ( i .LE. n )
280  IF( i.LT.n .AND. ipiv(i) .LT. 0 ) THEN
281  e(i)=a(i+1,i)
282  e(i+1)=zero
283  a(i+1,i)=zero
284  i=i+1
285  ELSE
286  e(i)=zero
287  ENDIF
288  i=i+1
289  END DO
290 *
291 * Convert PERMUTATIONS
292 *
293  i=1
294  DO WHILE ( i .LE. n )
295  IF( ipiv(i) .GT. 0 ) THEN
296  ip=ipiv(i)
297  IF (i .GT. 1) THEN
298  DO 22 j= 1,i-1
299  temp=a(ip,j)
300  a(ip,j)=a(i,j)
301  a(i,j)=temp
302  22 CONTINUE
303  ENDIF
304  ELSE
305  ip=-ipiv(i)
306  IF (i .GT. 1) THEN
307  DO 23 j= 1,i-1
308  temp=a(ip,j)
309  a(ip,j)=a(i+1,j)
310  a(i+1,j)=temp
311  23 CONTINUE
312  ENDIF
313  i=i+1
314  ENDIF
315  i=i+1
316  END DO
317  ELSE
318 *
319 * Revert A (A is lower)
320 *
321 *
322 * Revert PERMUTATIONS
323 *
324  i=n
325  DO WHILE ( i .GE. 1 )
326  IF( ipiv(i) .GT. 0 ) THEN
327  ip=ipiv(i)
328  IF (i .GT. 1) THEN
329  DO j= 1,i-1
330  temp=a(i,j)
331  a(i,j)=a(ip,j)
332  a(ip,j)=temp
333  END DO
334  ENDIF
335  ELSE
336  ip=-ipiv(i)
337  i=i-1
338  IF (i .GT. 1) THEN
339  DO j= 1,i-1
340  temp=a(i+1,j)
341  a(i+1,j)=a(ip,j)
342  a(ip,j)=temp
343  END DO
344  ENDIF
345  ENDIF
346  i=i-1
347  END DO
348 *
349 * Revert VALUE
350 *
351  i=1
352  DO WHILE ( i .LE. n-1 )
353  IF( ipiv(i) .LT. 0 ) THEN
354  a(i+1,i)=e(i)
355  i=i+1
356  ENDIF
357  i=i+1
358  END DO
359  END IF
360  END IF
361 
362  RETURN
363 *
364 * End of SSYCONV
365 *
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xerbla
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
lsame
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55