LAPACK  3.9.1
LAPACK: Linear Algebra PACKage

◆ zsyr2k()

subroutine zsyr2k ( character  UPLO,
character  TRANS,
integer  N,
integer  K,
complex*16  ALPHA,
complex*16, dimension(lda,*)  A,
integer  LDA,
complex*16, dimension(ldb,*)  B,
integer  LDB,
complex*16  BETA,
complex*16, dimension(ldc,*)  C,
integer  LDC 
)

ZSYR2K

Purpose:
 ZSYR2K  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.
[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',  K  specifies  the number of rows of the
           matrices  A and B.  K must be at least zero.
[in]ALPHA
          ALPHA is COMPLEX*16
           On entry, ALPHA specifies the scalar alpha.
[in]A
          A is COMPLEX*16 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 COMPLEX*16 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 COMPLEX*16
           On entry, BETA specifies the scalar beta.
[in,out]C
          C is COMPLEX*16 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 187 of file zsyr2k.f.

188 *
189 * -- Reference BLAS level3 routine --
190 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
191 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
192 *
193 * .. Scalar Arguments ..
194  COMPLEX*16 ALPHA,BETA
195  INTEGER K,LDA,LDB,LDC,N
196  CHARACTER TRANS,UPLO
197 * ..
198 * .. Array Arguments ..
199  COMPLEX*16 A(LDA,*),B(LDB,*),C(LDC,*)
200 * ..
201 *
202 * =====================================================================
203 *
204 * .. External Functions ..
205  LOGICAL LSAME
206  EXTERNAL lsame
207 * ..
208 * .. External Subroutines ..
209  EXTERNAL xerbla
210 * ..
211 * .. Intrinsic Functions ..
212  INTRINSIC max
213 * ..
214 * .. Local Scalars ..
215  COMPLEX*16 TEMP1,TEMP2
216  INTEGER I,INFO,J,L,NROWA
217  LOGICAL UPPER
218 * ..
219 * .. Parameters ..
220  COMPLEX*16 ONE
221  parameter(one= (1.0d+0,0.0d+0))
222  COMPLEX*16 ZERO
223  parameter(zero= (0.0d+0,0.0d+0))
224 * ..
225 *
226 * Test the input parameters.
227 *
228  IF (lsame(trans,'N')) THEN
229  nrowa = n
230  ELSE
231  nrowa = k
232  END IF
233  upper = lsame(uplo,'U')
234 *
235  info = 0
236  IF ((.NOT.upper) .AND. (.NOT.lsame(uplo,'L'))) THEN
237  info = 1
238  ELSE IF ((.NOT.lsame(trans,'N')) .AND.
239  + (.NOT.lsame(trans,'T'))) THEN
240  info = 2
241  ELSE IF (n.LT.0) THEN
242  info = 3
243  ELSE IF (k.LT.0) THEN
244  info = 4
245  ELSE IF (lda.LT.max(1,nrowa)) THEN
246  info = 7
247  ELSE IF (ldb.LT.max(1,nrowa)) THEN
248  info = 9
249  ELSE IF (ldc.LT.max(1,n)) THEN
250  info = 12
251  END IF
252  IF (info.NE.0) THEN
253  CALL xerbla('ZSYR2K',info)
254  RETURN
255  END IF
256 *
257 * Quick return if possible.
258 *
259  IF ((n.EQ.0) .OR. (((alpha.EQ.zero).OR.
260  + (k.EQ.0)).AND. (beta.EQ.one))) RETURN
261 *
262 * And when alpha.eq.zero.
263 *
264  IF (alpha.EQ.zero) THEN
265  IF (upper) THEN
266  IF (beta.EQ.zero) THEN
267  DO 20 j = 1,n
268  DO 10 i = 1,j
269  c(i,j) = zero
270  10 CONTINUE
271  20 CONTINUE
272  ELSE
273  DO 40 j = 1,n
274  DO 30 i = 1,j
275  c(i,j) = beta*c(i,j)
276  30 CONTINUE
277  40 CONTINUE
278  END IF
279  ELSE
280  IF (beta.EQ.zero) THEN
281  DO 60 j = 1,n
282  DO 50 i = j,n
283  c(i,j) = zero
284  50 CONTINUE
285  60 CONTINUE
286  ELSE
287  DO 80 j = 1,n
288  DO 70 i = j,n
289  c(i,j) = beta*c(i,j)
290  70 CONTINUE
291  80 CONTINUE
292  END IF
293  END IF
294  RETURN
295  END IF
296 *
297 * Start the operations.
298 *
299  IF (lsame(trans,'N')) THEN
300 *
301 * Form C := alpha*A*B**T + alpha*B*A**T + C.
302 *
303  IF (upper) THEN
304  DO 130 j = 1,n
305  IF (beta.EQ.zero) THEN
306  DO 90 i = 1,j
307  c(i,j) = zero
308  90 CONTINUE
309  ELSE IF (beta.NE.one) THEN
310  DO 100 i = 1,j
311  c(i,j) = beta*c(i,j)
312  100 CONTINUE
313  END IF
314  DO 120 l = 1,k
315  IF ((a(j,l).NE.zero) .OR. (b(j,l).NE.zero)) THEN
316  temp1 = alpha*b(j,l)
317  temp2 = alpha*a(j,l)
318  DO 110 i = 1,j
319  c(i,j) = c(i,j) + a(i,l)*temp1 +
320  + b(i,l)*temp2
321  110 CONTINUE
322  END IF
323  120 CONTINUE
324  130 CONTINUE
325  ELSE
326  DO 180 j = 1,n
327  IF (beta.EQ.zero) THEN
328  DO 140 i = j,n
329  c(i,j) = zero
330  140 CONTINUE
331  ELSE IF (beta.NE.one) THEN
332  DO 150 i = j,n
333  c(i,j) = beta*c(i,j)
334  150 CONTINUE
335  END IF
336  DO 170 l = 1,k
337  IF ((a(j,l).NE.zero) .OR. (b(j,l).NE.zero)) THEN
338  temp1 = alpha*b(j,l)
339  temp2 = alpha*a(j,l)
340  DO 160 i = j,n
341  c(i,j) = c(i,j) + a(i,l)*temp1 +
342  + b(i,l)*temp2
343  160 CONTINUE
344  END IF
345  170 CONTINUE
346  180 CONTINUE
347  END IF
348  ELSE
349 *
350 * Form C := alpha*A**T*B + alpha*B**T*A + C.
351 *
352  IF (upper) THEN
353  DO 210 j = 1,n
354  DO 200 i = 1,j
355  temp1 = zero
356  temp2 = zero
357  DO 190 l = 1,k
358  temp1 = temp1 + a(l,i)*b(l,j)
359  temp2 = temp2 + b(l,i)*a(l,j)
360  190 CONTINUE
361  IF (beta.EQ.zero) THEN
362  c(i,j) = alpha*temp1 + alpha*temp2
363  ELSE
364  c(i,j) = beta*c(i,j) + alpha*temp1 +
365  + alpha*temp2
366  END IF
367  200 CONTINUE
368  210 CONTINUE
369  ELSE
370  DO 240 j = 1,n
371  DO 230 i = j,n
372  temp1 = zero
373  temp2 = zero
374  DO 220 l = 1,k
375  temp1 = temp1 + a(l,i)*b(l,j)
376  temp2 = temp2 + b(l,i)*a(l,j)
377  220 CONTINUE
378  IF (beta.EQ.zero) THEN
379  c(i,j) = alpha*temp1 + alpha*temp2
380  ELSE
381  c(i,j) = beta*c(i,j) + alpha*temp1 +
382  + alpha*temp2
383  END IF
384  230 CONTINUE
385  240 CONTINUE
386  END IF
387  END IF
388 *
389  RETURN
390 *
391 * End of ZSYR2K.
392 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
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