LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 subroutine sorg2r ( integer M, integer N, integer K, real, dimension( lda, * ) A, integer LDA, real, dimension( * ) TAU, real, dimension( * ) WORK, integer INFO )

SORG2R generates all or part of the orthogonal matrix Q from a QR factorization determined by sgeqrf (unblocked algorithm).

Purpose:
SORG2R generates an m by n real matrix Q with orthonormal columns,
which is defined as the first n columns of a product of k elementary
reflectors of order m

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

as returned by SGEQRF.
Parameters
 [in] M M is INTEGER The number of rows of the matrix Q. M >= 0. [in] N N is INTEGER The number of columns of the matrix Q. M >= N >= 0. [in] K K is INTEGER The number of elementary reflectors whose product defines the matrix Q. N >= K >= 0. [in,out] A A is REAL array, dimension (LDA,N) On entry, the i-th column must contain the vector which defines the elementary reflector H(i), for i = 1,2,...,k, as returned by SGEQRF in the first k columns of its array argument A. On exit, the m-by-n matrix Q. [in] LDA LDA is INTEGER The first dimension of the array A. LDA >= max(1,M). [in] TAU TAU is REAL array, dimension (K) TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by SGEQRF. [out] WORK WORK is REAL array, dimension (N) [out] INFO INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument has an illegal value
Date
September 2012

Definition at line 116 of file sorg2r.f.

116 *
117 * -- LAPACK computational routine (version 3.4.2) --
118 * -- LAPACK is a software package provided by Univ. of Tennessee, --
119 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
120 * September 2012
121 *
122 * .. Scalar Arguments ..
123  INTEGER info, k, lda, m, n
124 * ..
125 * .. Array Arguments ..
126  REAL a( lda, * ), tau( * ), work( * )
127 * ..
128 *
129 * =====================================================================
130 *
131 * .. Parameters ..
132  REAL one, zero
133  parameter ( one = 1.0e+0, zero = 0.0e+0 )
134 * ..
135 * .. Local Scalars ..
136  INTEGER i, j, l
137 * ..
138 * .. External Subroutines ..
139  EXTERNAL slarf, sscal, xerbla
140 * ..
141 * .. Intrinsic Functions ..
142  INTRINSIC max
143 * ..
144 * .. Executable Statements ..
145 *
146 * Test the input arguments
147 *
148  info = 0
149  IF( m.LT.0 ) THEN
150  info = -1
151  ELSE IF( n.LT.0 .OR. n.GT.m ) THEN
152  info = -2
153  ELSE IF( k.LT.0 .OR. k.GT.n ) THEN
154  info = -3
155  ELSE IF( lda.LT.max( 1, m ) ) THEN
156  info = -5
157  END IF
158  IF( info.NE.0 ) THEN
159  CALL xerbla( 'SORG2R', -info )
160  RETURN
161  END IF
162 *
163 * Quick return if possible
164 *
165  IF( n.LE.0 )
166  \$ RETURN
167 *
168 * Initialise columns k+1:n to columns of the unit matrix
169 *
170  DO 20 j = k + 1, n
171  DO 10 l = 1, m
172  a( l, j ) = zero
173  10 CONTINUE
174  a( j, j ) = one
175  20 CONTINUE
176 *
177  DO 40 i = k, 1, -1
178 *
179 * Apply H(i) to A(i:m,i:n) from the left
180 *
181  IF( i.LT.n ) THEN
182  a( i, i ) = one
183  CALL slarf( 'Left', m-i+1, n-i, a( i, i ), 1, tau( i ),
184  \$ a( i, i+1 ), lda, work )
185  END IF
186  IF( i.LT.m )
187  \$ CALL sscal( m-i, -tau( i ), a( i+1, i ), 1 )
188  a( i, i ) = one - tau( i )
189 *
190 * Set A(1:i-1,i) to zero
191 *
192  DO 30 l = 1, i - 1
193  a( l, i ) = zero
194  30 CONTINUE
195  40 CONTINUE
196  RETURN
197 *
198 * End of SORG2R
199 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine slarf(SIDE, M, N, V, INCV, TAU, C, LDC, WORK)
SLARF applies an elementary reflector to a general rectangular matrix.
Definition: slarf.f:126
subroutine sscal(N, SA, SX, INCX)
SSCAL
Definition: sscal.f:55

Here is the call graph for this function:

Here is the caller graph for this function: