LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ sorm2l()

subroutine sorm2l ( character  side,
character  trans,
integer  m,
integer  n,
integer  k,
real, dimension( lda, * )  a,
integer  lda,
real, dimension( * )  tau,
real, dimension( ldc, * )  c,
integer  ldc,
real, dimension( * )  work,
integer  info 
)

SORM2L multiplies a general matrix by the orthogonal matrix from a QL factorization determined by sgeqlf (unblocked algorithm).

Download SORM2L + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SORM2L overwrites the general real m by n matrix C with

       Q * C  if SIDE = 'L' and TRANS = 'N', or

       Q**T * C  if SIDE = 'L' and TRANS = 'T', or

       C * Q  if SIDE = 'R' and TRANS = 'N', or

       C * Q**T if SIDE = 'R' and TRANS = 'T',

 where Q is a real orthogonal matrix defined as the product of k
 elementary reflectors

       Q = H(k) . . . H(2) H(1)

 as returned by SGEQLF. Q is of order m if SIDE = 'L' and of order n
 if SIDE = 'R'.
Parameters
[in]SIDE
          SIDE is CHARACTER*1
          = 'L': apply Q or Q**T from the Left
          = 'R': apply Q or Q**T from the Right
[in]TRANS
          TRANS is CHARACTER*1
          = 'N': apply Q  (No transpose)
          = 'T': apply Q**T (Transpose)
[in]M
          M is INTEGER
          The number of rows of the matrix C. M >= 0.
[in]N
          N is INTEGER
          The number of columns of the matrix C. N >= 0.
[in]K
          K is INTEGER
          The number of elementary reflectors whose product defines
          the matrix Q.
          If SIDE = 'L', M >= K >= 0;
          if SIDE = 'R', N >= K >= 0.
[in]A
          A is REAL array, dimension (LDA,K)
          The i-th column must contain the vector which defines the
          elementary reflector H(i), for i = 1,2,...,k, as returned by
          SGEQLF in the last k columns of its array argument A.
          A is modified by the routine but restored on exit.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.
          If SIDE = 'L', LDA >= max(1,M);
          if SIDE = 'R', LDA >= max(1,N).
[in]TAU
          TAU is REAL array, dimension (K)
          TAU(i) must contain the scalar factor of the elementary
          reflector H(i), as returned by SGEQLF.
[in,out]C
          C is REAL array, dimension (LDC,N)
          On entry, the m by n matrix C.
          On exit, C is overwritten by Q*C or Q**T*C or C*Q**T or C*Q.
[in]LDC
          LDC is INTEGER
          The leading dimension of the array C. LDC >= max(1,M).
[out]WORK
          WORK is REAL array, dimension
                                   (N) if SIDE = 'L',
                                   (M) if SIDE = 'R'
[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.

Definition at line 157 of file sorm2l.f.

159*
160* -- LAPACK computational routine --
161* -- LAPACK is a software package provided by Univ. of Tennessee, --
162* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
163*
164* .. Scalar Arguments ..
165 CHARACTER SIDE, TRANS
166 INTEGER INFO, K, LDA, LDC, M, N
167* ..
168* .. Array Arguments ..
169 REAL A( LDA, * ), C( LDC, * ), TAU( * ), WORK( * )
170* ..
171*
172* =====================================================================
173*
174* .. Parameters ..
175 REAL ONE
176 parameter( one = 1.0e+0 )
177* ..
178* .. Local Scalars ..
179 LOGICAL LEFT, NOTRAN
180 INTEGER I, I1, I2, I3, MI, NI, NQ
181 REAL AII
182* ..
183* .. External Functions ..
184 LOGICAL LSAME
185 EXTERNAL lsame
186* ..
187* .. External Subroutines ..
188 EXTERNAL slarf, xerbla
189* ..
190* .. Intrinsic Functions ..
191 INTRINSIC max
192* ..
193* .. Executable Statements ..
194*
195* Test the input arguments
196*
197 info = 0
198 left = lsame( side, 'L' )
199 notran = lsame( trans, 'N' )
200*
201* NQ is the order of Q
202*
203 IF( left ) THEN
204 nq = m
205 ELSE
206 nq = n
207 END IF
208 IF( .NOT.left .AND. .NOT.lsame( side, 'R' ) ) THEN
209 info = -1
210 ELSE IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) ) THEN
211 info = -2
212 ELSE IF( m.LT.0 ) THEN
213 info = -3
214 ELSE IF( n.LT.0 ) THEN
215 info = -4
216 ELSE IF( k.LT.0 .OR. k.GT.nq ) THEN
217 info = -5
218 ELSE IF( lda.LT.max( 1, nq ) ) THEN
219 info = -7
220 ELSE IF( ldc.LT.max( 1, m ) ) THEN
221 info = -10
222 END IF
223 IF( info.NE.0 ) THEN
224 CALL xerbla( 'SORM2L', -info )
225 RETURN
226 END IF
227*
228* Quick return if possible
229*
230 IF( m.EQ.0 .OR. n.EQ.0 .OR. k.EQ.0 )
231 $ RETURN
232*
233 IF( ( left .AND. notran ) .OR. ( .NOT.left .AND. .NOT.notran ) )
234 $ THEN
235 i1 = 1
236 i2 = k
237 i3 = 1
238 ELSE
239 i1 = k
240 i2 = 1
241 i3 = -1
242 END IF
243*
244 IF( left ) THEN
245 ni = n
246 ELSE
247 mi = m
248 END IF
249*
250 DO 10 i = i1, i2, i3
251 IF( left ) THEN
252*
253* H(i) is applied to C(1:m-k+i,1:n)
254*
255 mi = m - k + i
256 ELSE
257*
258* H(i) is applied to C(1:m,1:n-k+i)
259*
260 ni = n - k + i
261 END IF
262*
263* Apply H(i)
264*
265 aii = a( nq-k+i, i )
266 a( nq-k+i, i ) = one
267 CALL slarf( side, mi, ni, a( 1, i ), 1, tau( i ), c, ldc,
268 $ work )
269 a( nq-k+i, i ) = aii
270 10 CONTINUE
271 RETURN
272*
273* End of SORM2L
274*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine slarf(side, m, n, v, incv, tau, c, ldc, work)
SLARF applies an elementary reflector to a general rectangular matrix.
Definition slarf.f:124
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
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