 LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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## ◆ cunbdb5()

 subroutine cunbdb5 ( integer M1, integer M2, integer N, complex, dimension(*) X1, integer INCX1, complex, dimension(*) X2, integer INCX2, complex, dimension(ldq1,*) Q1, integer LDQ1, complex, dimension(ldq2,*) Q2, integer LDQ2, complex, dimension(*) WORK, integer LWORK, integer INFO )

CUNBDB5

Purpose:
``` CUNBDB5 orthogonalizes the column vector
X = [ X1 ]
[ X2 ]
with respect to the columns of
Q = [ Q1 ] .
[ Q2 ]
The columns of Q must be orthonormal.

If the projection is zero according to Kahan's "twice is enough"
criterion, then some other vector from the orthogonal complement
is returned. This vector is chosen in an arbitrary but deterministic
way.```
Parameters
 [in] M1 ``` M1 is INTEGER The dimension of X1 and the number of rows in Q1. 0 <= M1.``` [in] M2 ``` M2 is INTEGER The dimension of X2 and the number of rows in Q2. 0 <= M2.``` [in] N ``` N is INTEGER The number of columns in Q1 and Q2. 0 <= N.``` [in,out] X1 ``` X1 is COMPLEX array, dimension (M1) On entry, the top part of the vector to be orthogonalized. On exit, the top part of the projected vector.``` [in] INCX1 ``` INCX1 is INTEGER Increment for entries of X1.``` [in,out] X2 ``` X2 is COMPLEX array, dimension (M2) On entry, the bottom part of the vector to be orthogonalized. On exit, the bottom part of the projected vector.``` [in] INCX2 ``` INCX2 is INTEGER Increment for entries of X2.``` [in] Q1 ``` Q1 is COMPLEX array, dimension (LDQ1, N) The top part of the orthonormal basis matrix.``` [in] LDQ1 ``` LDQ1 is INTEGER The leading dimension of Q1. LDQ1 >= M1.``` [in] Q2 ``` Q2 is COMPLEX array, dimension (LDQ2, N) The bottom part of the orthonormal basis matrix.``` [in] LDQ2 ``` LDQ2 is INTEGER The leading dimension of Q2. LDQ2 >= M2.``` [out] WORK ` WORK is COMPLEX array, dimension (LWORK)` [in] LWORK ``` LWORK is INTEGER The dimension of the array WORK. LWORK >= N.``` [out] INFO ``` INFO is INTEGER = 0: successful exit. < 0: if INFO = -i, the i-th argument had an illegal value.```

Definition at line 154 of file cunbdb5.f.

156*
157* -- LAPACK computational routine --
158* -- LAPACK is a software package provided by Univ. of Tennessee, --
159* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
160*
161* .. Scalar Arguments ..
162 INTEGER INCX1, INCX2, INFO, LDQ1, LDQ2, LWORK, M1, M2,
163 \$ N
164* ..
165* .. Array Arguments ..
166 COMPLEX Q1(LDQ1,*), Q2(LDQ2,*), WORK(*), X1(*), X2(*)
167* ..
168*
169* =====================================================================
170*
171* .. Parameters ..
172 COMPLEX ONE, ZERO
173 parameter( one = (1.0e0,0.0e0), zero = (0.0e0,0.0e0) )
174* ..
175* .. Local Scalars ..
176 INTEGER CHILDINFO, I, J
177* ..
178* .. External Subroutines ..
179 EXTERNAL cunbdb6, xerbla
180* ..
181* .. External Functions ..
182 REAL SCNRM2
183 EXTERNAL scnrm2
184* ..
185* .. Intrinsic Function ..
186 INTRINSIC max
187* ..
188* .. Executable Statements ..
189*
190* Test input arguments
191*
192 info = 0
193 IF( m1 .LT. 0 ) THEN
194 info = -1
195 ELSE IF( m2 .LT. 0 ) THEN
196 info = -2
197 ELSE IF( n .LT. 0 ) THEN
198 info = -3
199 ELSE IF( incx1 .LT. 1 ) THEN
200 info = -5
201 ELSE IF( incx2 .LT. 1 ) THEN
202 info = -7
203 ELSE IF( ldq1 .LT. max( 1, m1 ) ) THEN
204 info = -9
205 ELSE IF( ldq2 .LT. max( 1, m2 ) ) THEN
206 info = -11
207 ELSE IF( lwork .LT. n ) THEN
208 info = -13
209 END IF
210*
211 IF( info .NE. 0 ) THEN
212 CALL xerbla( 'CUNBDB5', -info )
213 RETURN
214 END IF
215*
216* Project X onto the orthogonal complement of Q
217*
218 CALL cunbdb6( m1, m2, n, x1, incx1, x2, incx2, q1, ldq1, q2, ldq2,
219 \$ work, lwork, childinfo )
220*
221* If the projection is nonzero, then return
222*
223 IF( scnrm2(m1,x1,incx1) .NE. zero
224 \$ .OR. scnrm2(m2,x2,incx2) .NE. zero ) THEN
225 RETURN
226 END IF
227*
228* Project each standard basis vector e_1,...,e_M1 in turn, stopping
229* when a nonzero projection is found
230*
231 DO i = 1, m1
232 DO j = 1, m1
233 x1(j) = zero
234 END DO
235 x1(i) = one
236 DO j = 1, m2
237 x2(j) = zero
238 END DO
239 CALL cunbdb6( m1, m2, n, x1, incx1, x2, incx2, q1, ldq1, q2,
240 \$ ldq2, work, lwork, childinfo )
241 IF( scnrm2(m1,x1,incx1) .NE. zero
242 \$ .OR. scnrm2(m2,x2,incx2) .NE. zero ) THEN
243 RETURN
244 END IF
245 END DO
246*
247* Project each standard basis vector e_(M1+1),...,e_(M1+M2) in turn,
248* stopping when a nonzero projection is found
249*
250 DO i = 1, m2
251 DO j = 1, m1
252 x1(j) = zero
253 END DO
254 DO j = 1, m2
255 x2(j) = zero
256 END DO
257 x2(i) = one
258 CALL cunbdb6( m1, m2, n, x1, incx1, x2, incx2, q1, ldq1, q2,
259 \$ ldq2, work, lwork, childinfo )
260 IF( scnrm2(m1,x1,incx1) .NE. zero
261 \$ .OR. scnrm2(m2,x2,incx2) .NE. zero ) THEN
262 RETURN
263 END IF
264 END DO
265*
266 RETURN
267*
268* End of CUNBDB5
269*
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine cunbdb6(M1, M2, N, X1, INCX1, X2, INCX2, Q1, LDQ1, Q2, LDQ2, WORK, LWORK, INFO)
CUNBDB6
Definition: cunbdb6.f:160
real(wp) function scnrm2(n, x, incx)
SCNRM2
Definition: scnrm2.f90:90
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