LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ dsyr2k()

subroutine dsyr2k ( character  UPLO,
character  TRANS,
integer  N,
integer  K,
double precision  ALPHA,
double precision, dimension(lda,*)  A,
integer  LDA,
double precision, dimension(ldb,*)  B,
integer  LDB,
double precision  BETA,
double precision, dimension(ldc,*)  C,
integer  LDC 
)

DSYR2K

Purpose:
 DSYR2K  performs one of the symmetric rank 2k operations

    C := alpha*A*B**T + alpha*B*A**T + beta*C,

 or

    C := alpha*A**T*B + alpha*B**T*A + beta*C,

 where  alpha and beta  are scalars, C is an  n by n  symmetric matrix
 and  A and B  are  n by k  matrices  in the  first  case  and  k by n
 matrices in the second case.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
           On  entry,   UPLO  specifies  whether  the  upper  or  lower
           triangular  part  of the  array  C  is to be  referenced  as
           follows:

              UPLO = 'U' or 'u'   Only the  upper triangular part of  C
                                  is to be referenced.

              UPLO = 'L' or 'l'   Only the  lower triangular part of  C
                                  is to be referenced.
[in]TRANS
          TRANS is CHARACTER*1
           On entry,  TRANS  specifies the operation to be performed as
           follows:

              TRANS = 'N' or 'n'   C := alpha*A*B**T + alpha*B*A**T +
                                        beta*C.

              TRANS = 'T' or 't'   C := alpha*A**T*B + alpha*B**T*A +
                                        beta*C.

              TRANS = 'C' or 'c'   C := alpha*A**T*B + alpha*B**T*A +
                                        beta*C.
[in]N
          N is INTEGER
           On entry,  N specifies the order of the matrix C.  N must be
           at least zero.
[in]K
          K is INTEGER
           On entry with  TRANS = 'N' or 'n',  K  specifies  the number
           of  columns  of the  matrices  A and B,  and on  entry  with
           TRANS = 'T' or 't' or 'C' or 'c',  K  specifies  the  number
           of rows of the matrices  A and B.  K must be at least  zero.
[in]ALPHA
          ALPHA is DOUBLE PRECISION.
           On entry, ALPHA specifies the scalar alpha.
[in]A
          A is DOUBLE PRECISION array, dimension ( LDA, ka ), where ka is
           k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
           Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
           part of the array  A  must contain the matrix  A,  otherwise
           the leading  k by n  part of the array  A  must contain  the
           matrix A.
[in]LDA
          LDA is INTEGER
           On entry, LDA specifies the first dimension of A as declared
           in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
           then  LDA must be at least  max( 1, n ), otherwise  LDA must
           be at least  max( 1, k ).
[in]B
          B is DOUBLE PRECISION array, dimension ( LDB, kb ), where kb is
           k  when  TRANS = 'N' or 'n',  and is  n  otherwise.
           Before entry with  TRANS = 'N' or 'n',  the  leading  n by k
           part of the array  B  must contain the matrix  B,  otherwise
           the leading  k by n  part of the array  B  must contain  the
           matrix B.
[in]LDB
          LDB is INTEGER
           On entry, LDB specifies the first dimension of B as declared
           in  the  calling  (sub)  program.   When  TRANS = 'N' or 'n'
           then  LDB must be at least  max( 1, n ), otherwise  LDB must
           be at least  max( 1, k ).
[in]BETA
          BETA is DOUBLE PRECISION.
           On entry, BETA specifies the scalar beta.
[in,out]C
          C is DOUBLE PRECISION array, dimension ( LDC, N )
           Before entry  with  UPLO = 'U' or 'u',  the leading  n by n
           upper triangular part of the array C must contain the upper
           triangular part  of the  symmetric matrix  and the strictly
           lower triangular part of C is not referenced.  On exit, the
           upper triangular part of the array  C is overwritten by the
           upper triangular part of the updated matrix.
           Before entry  with  UPLO = 'L' or 'l',  the leading  n by n
           lower triangular part of the array C must contain the lower
           triangular part  of the  symmetric matrix  and the strictly
           upper triangular part of C is not referenced.  On exit, the
           lower triangular part of the array  C is overwritten by the
           lower triangular part of the updated matrix.
[in]LDC
          LDC is INTEGER
           On entry, LDC specifies the first dimension of C as declared
           in  the  calling  (sub)  program.   LDC  must  be  at  least
           max( 1, n ).
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Further Details:
  Level 3 Blas routine.


  -- Written on 8-February-1989.
     Jack Dongarra, Argonne National Laboratory.
     Iain Duff, AERE Harwell.
     Jeremy Du Croz, Numerical Algorithms Group Ltd.
     Sven Hammarling, Numerical Algorithms Group Ltd.

Definition at line 191 of file dsyr2k.f.

192 *
193 * -- Reference BLAS level3 routine --
194 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
195 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
196 *
197 * .. Scalar Arguments ..
198  DOUBLE PRECISION ALPHA,BETA
199  INTEGER K,LDA,LDB,LDC,N
200  CHARACTER TRANS,UPLO
201 * ..
202 * .. Array Arguments ..
203  DOUBLE PRECISION A(LDA,*),B(LDB,*),C(LDC,*)
204 * ..
205 *
206 * =====================================================================
207 *
208 * .. External Functions ..
209  LOGICAL LSAME
210  EXTERNAL lsame
211 * ..
212 * .. External Subroutines ..
213  EXTERNAL xerbla
214 * ..
215 * .. Intrinsic Functions ..
216  INTRINSIC max
217 * ..
218 * .. Local Scalars ..
219  DOUBLE PRECISION TEMP1,TEMP2
220  INTEGER I,INFO,J,L,NROWA
221  LOGICAL UPPER
222 * ..
223 * .. Parameters ..
224  DOUBLE PRECISION ONE,ZERO
225  parameter(one=1.0d+0,zero=0.0d+0)
226 * ..
227 *
228 * Test the input parameters.
229 *
230  IF (lsame(trans,'N')) THEN
231  nrowa = n
232  ELSE
233  nrowa = k
234  END IF
235  upper = lsame(uplo,'U')
236 *
237  info = 0
238  IF ((.NOT.upper) .AND. (.NOT.lsame(uplo,'L'))) THEN
239  info = 1
240  ELSE IF ((.NOT.lsame(trans,'N')) .AND.
241  + (.NOT.lsame(trans,'T')) .AND.
242  + (.NOT.lsame(trans,'C'))) THEN
243  info = 2
244  ELSE IF (n.LT.0) THEN
245  info = 3
246  ELSE IF (k.LT.0) THEN
247  info = 4
248  ELSE IF (lda.LT.max(1,nrowa)) THEN
249  info = 7
250  ELSE IF (ldb.LT.max(1,nrowa)) THEN
251  info = 9
252  ELSE IF (ldc.LT.max(1,n)) THEN
253  info = 12
254  END IF
255  IF (info.NE.0) THEN
256  CALL xerbla('DSYR2K',info)
257  RETURN
258  END IF
259 *
260 * Quick return if possible.
261 *
262  IF ((n.EQ.0) .OR. (((alpha.EQ.zero).OR.
263  + (k.EQ.0)).AND. (beta.EQ.one))) RETURN
264 *
265 * And when alpha.eq.zero.
266 *
267  IF (alpha.EQ.zero) THEN
268  IF (upper) THEN
269  IF (beta.EQ.zero) THEN
270  DO 20 j = 1,n
271  DO 10 i = 1,j
272  c(i,j) = zero
273  10 CONTINUE
274  20 CONTINUE
275  ELSE
276  DO 40 j = 1,n
277  DO 30 i = 1,j
278  c(i,j) = beta*c(i,j)
279  30 CONTINUE
280  40 CONTINUE
281  END IF
282  ELSE
283  IF (beta.EQ.zero) THEN
284  DO 60 j = 1,n
285  DO 50 i = j,n
286  c(i,j) = zero
287  50 CONTINUE
288  60 CONTINUE
289  ELSE
290  DO 80 j = 1,n
291  DO 70 i = j,n
292  c(i,j) = beta*c(i,j)
293  70 CONTINUE
294  80 CONTINUE
295  END IF
296  END IF
297  RETURN
298  END IF
299 *
300 * Start the operations.
301 *
302  IF (lsame(trans,'N')) THEN
303 *
304 * Form C := alpha*A*B**T + alpha*B*A**T + C.
305 *
306  IF (upper) THEN
307  DO 130 j = 1,n
308  IF (beta.EQ.zero) THEN
309  DO 90 i = 1,j
310  c(i,j) = zero
311  90 CONTINUE
312  ELSE IF (beta.NE.one) THEN
313  DO 100 i = 1,j
314  c(i,j) = beta*c(i,j)
315  100 CONTINUE
316  END IF
317  DO 120 l = 1,k
318  IF ((a(j,l).NE.zero) .OR. (b(j,l).NE.zero)) THEN
319  temp1 = alpha*b(j,l)
320  temp2 = alpha*a(j,l)
321  DO 110 i = 1,j
322  c(i,j) = c(i,j) + a(i,l)*temp1 +
323  + b(i,l)*temp2
324  110 CONTINUE
325  END IF
326  120 CONTINUE
327  130 CONTINUE
328  ELSE
329  DO 180 j = 1,n
330  IF (beta.EQ.zero) THEN
331  DO 140 i = j,n
332  c(i,j) = zero
333  140 CONTINUE
334  ELSE IF (beta.NE.one) THEN
335  DO 150 i = j,n
336  c(i,j) = beta*c(i,j)
337  150 CONTINUE
338  END IF
339  DO 170 l = 1,k
340  IF ((a(j,l).NE.zero) .OR. (b(j,l).NE.zero)) THEN
341  temp1 = alpha*b(j,l)
342  temp2 = alpha*a(j,l)
343  DO 160 i = j,n
344  c(i,j) = c(i,j) + a(i,l)*temp1 +
345  + b(i,l)*temp2
346  160 CONTINUE
347  END IF
348  170 CONTINUE
349  180 CONTINUE
350  END IF
351  ELSE
352 *
353 * Form C := alpha*A**T*B + alpha*B**T*A + C.
354 *
355  IF (upper) THEN
356  DO 210 j = 1,n
357  DO 200 i = 1,j
358  temp1 = zero
359  temp2 = zero
360  DO 190 l = 1,k
361  temp1 = temp1 + a(l,i)*b(l,j)
362  temp2 = temp2 + b(l,i)*a(l,j)
363  190 CONTINUE
364  IF (beta.EQ.zero) THEN
365  c(i,j) = alpha*temp1 + alpha*temp2
366  ELSE
367  c(i,j) = beta*c(i,j) + alpha*temp1 +
368  + alpha*temp2
369  END IF
370  200 CONTINUE
371  210 CONTINUE
372  ELSE
373  DO 240 j = 1,n
374  DO 230 i = j,n
375  temp1 = zero
376  temp2 = zero
377  DO 220 l = 1,k
378  temp1 = temp1 + a(l,i)*b(l,j)
379  temp2 = temp2 + b(l,i)*a(l,j)
380  220 CONTINUE
381  IF (beta.EQ.zero) THEN
382  c(i,j) = alpha*temp1 + alpha*temp2
383  ELSE
384  c(i,j) = beta*c(i,j) + alpha*temp1 +
385  + alpha*temp2
386  END IF
387  230 CONTINUE
388  240 CONTINUE
389  END IF
390  END IF
391 *
392  RETURN
393 *
394 * End of DSYR2K
395 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
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