 LAPACK  3.10.0 LAPACK: Linear Algebra PACKage

◆ clasr()

 subroutine clasr ( character SIDE, character PIVOT, character DIRECT, integer M, integer N, real, dimension( * ) C, real, dimension( * ) S, complex, dimension( lda, * ) A, integer LDA )

CLASR applies a sequence of plane rotations to a general rectangular matrix.

Purpose:
CLASR applies a sequence of real plane rotations to a complex matrix
A, from either the left or the right.

When SIDE = 'L', the transformation takes the form

A := P*A

and when SIDE = 'R', the transformation takes the form

A := A*P**T

where P is an orthogonal matrix consisting of a sequence of z plane
rotations, with z = M when SIDE = 'L' and z = N when SIDE = 'R',
and P**T is the transpose of P.

When DIRECT = 'F' (Forward sequence), then

P = P(z-1) * ... * P(2) * P(1)

and when DIRECT = 'B' (Backward sequence), then

P = P(1) * P(2) * ... * P(z-1)

where P(k) is a plane rotation matrix defined by the 2-by-2 rotation

R(k) = (  c(k)  s(k) )
= ( -s(k)  c(k) ).

When PIVOT = 'V' (Variable pivot), the rotation is performed
for the plane (k,k+1), i.e., P(k) has the form

P(k) = (  1                                            )
(       ...                                     )
(              1                                )
(                   c(k)  s(k)                  )
(                  -s(k)  c(k)                  )
(                                1              )
(                                     ...       )
(                                            1  )

where R(k) appears as a rank-2 modification to the identity matrix in
rows and columns k and k+1.

When PIVOT = 'T' (Top pivot), the rotation is performed for the
plane (1,k+1), so P(k) has the form

P(k) = (  c(k)                    s(k)                 )
(         1                                     )
(              ...                              )
(                     1                         )
( -s(k)                    c(k)                 )
(                                 1             )
(                                      ...      )
(                                             1 )

where R(k) appears in rows and columns 1 and k+1.

Similarly, when PIVOT = 'B' (Bottom pivot), the rotation is
performed for the plane (k,z), giving P(k) the form

P(k) = ( 1                                             )
(      ...                                      )
(             1                                 )
(                  c(k)                    s(k) )
(                         1                     )
(                              ...              )
(                                     1         )
(                 -s(k)                    c(k) )

where R(k) appears in rows and columns k and z.  The rotations are
performed without ever forming P(k) explicitly.
Parameters
 [in] SIDE SIDE is CHARACTER*1 Specifies whether the plane rotation matrix P is applied to A on the left or the right. = 'L': Left, compute A := P*A = 'R': Right, compute A:= A*P**T [in] PIVOT PIVOT is CHARACTER*1 Specifies the plane for which P(k) is a plane rotation matrix. = 'V': Variable pivot, the plane (k,k+1) = 'T': Top pivot, the plane (1,k+1) = 'B': Bottom pivot, the plane (k,z) [in] DIRECT DIRECT is CHARACTER*1 Specifies whether P is a forward or backward sequence of plane rotations. = 'F': Forward, P = P(z-1)*...*P(2)*P(1) = 'B': Backward, P = P(1)*P(2)*...*P(z-1) [in] M M is INTEGER The number of rows of the matrix A. If m <= 1, an immediate return is effected. [in] N N is INTEGER The number of columns of the matrix A. If n <= 1, an immediate return is effected. [in] C C is REAL array, dimension (M-1) if SIDE = 'L' (N-1) if SIDE = 'R' The cosines c(k) of the plane rotations. [in] S S is REAL array, dimension (M-1) if SIDE = 'L' (N-1) if SIDE = 'R' The sines s(k) of the plane rotations. The 2-by-2 plane rotation part of the matrix P(k), R(k), has the form R(k) = ( c(k) s(k) ) ( -s(k) c(k) ). [in,out] A A is COMPLEX array, dimension (LDA,N) The M-by-N matrix A. On exit, A is overwritten by P*A if SIDE = 'R' or by A*P**T if SIDE = 'L'. [in] LDA LDA is INTEGER The leading dimension of the array A. LDA >= max(1,M).

Definition at line 199 of file clasr.f.

200 *
201 * -- LAPACK auxiliary routine --
202 * -- LAPACK is a software package provided by Univ. of Tennessee, --
203 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
204 *
205 * .. Scalar Arguments ..
206  CHARACTER DIRECT, PIVOT, SIDE
207  INTEGER LDA, M, N
208 * ..
209 * .. Array Arguments ..
210  REAL C( * ), S( * )
211  COMPLEX A( LDA, * )
212 * ..
213 *
214 * =====================================================================
215 *
216 * .. Parameters ..
217  REAL ONE, ZERO
218  parameter( one = 1.0e+0, zero = 0.0e+0 )
219 * ..
220 * .. Local Scalars ..
221  INTEGER I, INFO, J
222  REAL CTEMP, STEMP
223  COMPLEX TEMP
224 * ..
225 * .. Intrinsic Functions ..
226  INTRINSIC max
227 * ..
228 * .. External Functions ..
229  LOGICAL LSAME
230  EXTERNAL lsame
231 * ..
232 * .. External Subroutines ..
233  EXTERNAL xerbla
234 * ..
235 * .. Executable Statements ..
236 *
237 * Test the input parameters
238 *
239  info = 0
240  IF( .NOT.( lsame( side, 'L' ) .OR. lsame( side, 'R' ) ) ) THEN
241  info = 1
242  ELSE IF( .NOT.( lsame( pivot, 'V' ) .OR. lsame( pivot,
243  \$ 'T' ) .OR. lsame( pivot, 'B' ) ) ) THEN
244  info = 2
245  ELSE IF( .NOT.( lsame( direct, 'F' ) .OR. lsame( direct, 'B' ) ) )
246  \$ THEN
247  info = 3
248  ELSE IF( m.LT.0 ) THEN
249  info = 4
250  ELSE IF( n.LT.0 ) THEN
251  info = 5
252  ELSE IF( lda.LT.max( 1, m ) ) THEN
253  info = 9
254  END IF
255  IF( info.NE.0 ) THEN
256  CALL xerbla( 'CLASR ', info )
257  RETURN
258  END IF
259 *
260 * Quick return if possible
261 *
262  IF( ( m.EQ.0 ) .OR. ( n.EQ.0 ) )
263  \$ RETURN
264  IF( lsame( side, 'L' ) ) THEN
265 *
266 * Form P * A
267 *
268  IF( lsame( pivot, 'V' ) ) THEN
269  IF( lsame( direct, 'F' ) ) THEN
270  DO 20 j = 1, m - 1
271  ctemp = c( j )
272  stemp = s( j )
273  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
274  DO 10 i = 1, n
275  temp = a( j+1, i )
276  a( j+1, i ) = ctemp*temp - stemp*a( j, i )
277  a( j, i ) = stemp*temp + ctemp*a( j, i )
278  10 CONTINUE
279  END IF
280  20 CONTINUE
281  ELSE IF( lsame( direct, 'B' ) ) THEN
282  DO 40 j = m - 1, 1, -1
283  ctemp = c( j )
284  stemp = s( j )
285  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
286  DO 30 i = 1, n
287  temp = a( j+1, i )
288  a( j+1, i ) = ctemp*temp - stemp*a( j, i )
289  a( j, i ) = stemp*temp + ctemp*a( j, i )
290  30 CONTINUE
291  END IF
292  40 CONTINUE
293  END IF
294  ELSE IF( lsame( pivot, 'T' ) ) THEN
295  IF( lsame( direct, 'F' ) ) THEN
296  DO 60 j = 2, m
297  ctemp = c( j-1 )
298  stemp = s( j-1 )
299  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
300  DO 50 i = 1, n
301  temp = a( j, i )
302  a( j, i ) = ctemp*temp - stemp*a( 1, i )
303  a( 1, i ) = stemp*temp + ctemp*a( 1, i )
304  50 CONTINUE
305  END IF
306  60 CONTINUE
307  ELSE IF( lsame( direct, 'B' ) ) THEN
308  DO 80 j = m, 2, -1
309  ctemp = c( j-1 )
310  stemp = s( j-1 )
311  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
312  DO 70 i = 1, n
313  temp = a( j, i )
314  a( j, i ) = ctemp*temp - stemp*a( 1, i )
315  a( 1, i ) = stemp*temp + ctemp*a( 1, i )
316  70 CONTINUE
317  END IF
318  80 CONTINUE
319  END IF
320  ELSE IF( lsame( pivot, 'B' ) ) THEN
321  IF( lsame( direct, 'F' ) ) THEN
322  DO 100 j = 1, m - 1
323  ctemp = c( j )
324  stemp = s( j )
325  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
326  DO 90 i = 1, n
327  temp = a( j, i )
328  a( j, i ) = stemp*a( m, i ) + ctemp*temp
329  a( m, i ) = ctemp*a( m, i ) - stemp*temp
330  90 CONTINUE
331  END IF
332  100 CONTINUE
333  ELSE IF( lsame( direct, 'B' ) ) THEN
334  DO 120 j = m - 1, 1, -1
335  ctemp = c( j )
336  stemp = s( j )
337  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
338  DO 110 i = 1, n
339  temp = a( j, i )
340  a( j, i ) = stemp*a( m, i ) + ctemp*temp
341  a( m, i ) = ctemp*a( m, i ) - stemp*temp
342  110 CONTINUE
343  END IF
344  120 CONTINUE
345  END IF
346  END IF
347  ELSE IF( lsame( side, 'R' ) ) THEN
348 *
349 * Form A * P**T
350 *
351  IF( lsame( pivot, 'V' ) ) THEN
352  IF( lsame( direct, 'F' ) ) THEN
353  DO 140 j = 1, n - 1
354  ctemp = c( j )
355  stemp = s( j )
356  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
357  DO 130 i = 1, m
358  temp = a( i, j+1 )
359  a( i, j+1 ) = ctemp*temp - stemp*a( i, j )
360  a( i, j ) = stemp*temp + ctemp*a( i, j )
361  130 CONTINUE
362  END IF
363  140 CONTINUE
364  ELSE IF( lsame( direct, 'B' ) ) THEN
365  DO 160 j = n - 1, 1, -1
366  ctemp = c( j )
367  stemp = s( j )
368  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
369  DO 150 i = 1, m
370  temp = a( i, j+1 )
371  a( i, j+1 ) = ctemp*temp - stemp*a( i, j )
372  a( i, j ) = stemp*temp + ctemp*a( i, j )
373  150 CONTINUE
374  END IF
375  160 CONTINUE
376  END IF
377  ELSE IF( lsame( pivot, 'T' ) ) THEN
378  IF( lsame( direct, 'F' ) ) THEN
379  DO 180 j = 2, n
380  ctemp = c( j-1 )
381  stemp = s( j-1 )
382  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
383  DO 170 i = 1, m
384  temp = a( i, j )
385  a( i, j ) = ctemp*temp - stemp*a( i, 1 )
386  a( i, 1 ) = stemp*temp + ctemp*a( i, 1 )
387  170 CONTINUE
388  END IF
389  180 CONTINUE
390  ELSE IF( lsame( direct, 'B' ) ) THEN
391  DO 200 j = n, 2, -1
392  ctemp = c( j-1 )
393  stemp = s( j-1 )
394  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
395  DO 190 i = 1, m
396  temp = a( i, j )
397  a( i, j ) = ctemp*temp - stemp*a( i, 1 )
398  a( i, 1 ) = stemp*temp + ctemp*a( i, 1 )
399  190 CONTINUE
400  END IF
401  200 CONTINUE
402  END IF
403  ELSE IF( lsame( pivot, 'B' ) ) THEN
404  IF( lsame( direct, 'F' ) ) THEN
405  DO 220 j = 1, n - 1
406  ctemp = c( j )
407  stemp = s( j )
408  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
409  DO 210 i = 1, m
410  temp = a( i, j )
411  a( i, j ) = stemp*a( i, n ) + ctemp*temp
412  a( i, n ) = ctemp*a( i, n ) - stemp*temp
413  210 CONTINUE
414  END IF
415  220 CONTINUE
416  ELSE IF( lsame( direct, 'B' ) ) THEN
417  DO 240 j = n - 1, 1, -1
418  ctemp = c( j )
419  stemp = s( j )
420  IF( ( ctemp.NE.one ) .OR. ( stemp.NE.zero ) ) THEN
421  DO 230 i = 1, m
422  temp = a( i, j )
423  a( i, j ) = stemp*a( i, n ) + ctemp*temp
424  a( i, n ) = ctemp*a( i, n ) - stemp*temp
425  230 CONTINUE
426  END IF
427  240 CONTINUE
428  END IF
429  END IF
430  END IF
431 *
432  RETURN
433 *
434 * End of CLASR
435 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
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