Annotation of rpl/lapack/lapack/dtzrqf.f, revision 1.10
1.10 ! bertrand 1: *> \brief \b DTZRQF
! 2: *
! 3: * =========== DOCUMENTATION ===========
! 4: *
! 5: * Online html documentation available at
! 6: * http://www.netlib.org/lapack/explore-html/
! 7: *
! 8: *> \htmlonly
! 9: *> Download DTZRQF + dependencies
! 10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dtzrqf.f">
! 11: *> [TGZ]</a>
! 12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dtzrqf.f">
! 13: *> [ZIP]</a>
! 14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dtzrqf.f">
! 15: *> [TXT]</a>
! 16: *> \endhtmlonly
! 17: *
! 18: * Definition:
! 19: * ===========
! 20: *
! 21: * SUBROUTINE DTZRQF( M, N, A, LDA, TAU, INFO )
! 22: *
! 23: * .. Scalar Arguments ..
! 24: * INTEGER INFO, LDA, M, N
! 25: * ..
! 26: * .. Array Arguments ..
! 27: * DOUBLE PRECISION A( LDA, * ), TAU( * )
! 28: * ..
! 29: *
! 30: *
! 31: *> \par Purpose:
! 32: * =============
! 33: *>
! 34: *> \verbatim
! 35: *>
! 36: *> This routine is deprecated and has been replaced by routine DTZRZF.
! 37: *>
! 38: *> DTZRQF reduces the M-by-N ( M<=N ) real upper trapezoidal matrix A
! 39: *> to upper triangular form by means of orthogonal transformations.
! 40: *>
! 41: *> The upper trapezoidal matrix A is factored as
! 42: *>
! 43: *> A = ( R 0 ) * Z,
! 44: *>
! 45: *> where Z is an N-by-N orthogonal matrix and R is an M-by-M upper
! 46: *> triangular matrix.
! 47: *> \endverbatim
! 48: *
! 49: * Arguments:
! 50: * ==========
! 51: *
! 52: *> \param[in] M
! 53: *> \verbatim
! 54: *> M is INTEGER
! 55: *> The number of rows of the matrix A. M >= 0.
! 56: *> \endverbatim
! 57: *>
! 58: *> \param[in] N
! 59: *> \verbatim
! 60: *> N is INTEGER
! 61: *> The number of columns of the matrix A. N >= M.
! 62: *> \endverbatim
! 63: *>
! 64: *> \param[in,out] A
! 65: *> \verbatim
! 66: *> A is DOUBLE PRECISION array, dimension (LDA,N)
! 67: *> On entry, the leading M-by-N upper trapezoidal part of the
! 68: *> array A must contain the matrix to be factorized.
! 69: *> On exit, the leading M-by-M upper triangular part of A
! 70: *> contains the upper triangular matrix R, and elements M+1 to
! 71: *> N of the first M rows of A, with the array TAU, represent the
! 72: *> orthogonal matrix Z as a product of M elementary reflectors.
! 73: *> \endverbatim
! 74: *>
! 75: *> \param[in] LDA
! 76: *> \verbatim
! 77: *> LDA is INTEGER
! 78: *> The leading dimension of the array A. LDA >= max(1,M).
! 79: *> \endverbatim
! 80: *>
! 81: *> \param[out] TAU
! 82: *> \verbatim
! 83: *> TAU is DOUBLE PRECISION array, dimension (M)
! 84: *> The scalar factors of the elementary reflectors.
! 85: *> \endverbatim
! 86: *>
! 87: *> \param[out] INFO
! 88: *> \verbatim
! 89: *> INFO is INTEGER
! 90: *> = 0: successful exit
! 91: *> < 0: if INFO = -i, the i-th argument had an illegal value
! 92: *> \endverbatim
! 93: *
! 94: * Authors:
! 95: * ========
! 96: *
! 97: *> \author Univ. of Tennessee
! 98: *> \author Univ. of California Berkeley
! 99: *> \author Univ. of Colorado Denver
! 100: *> \author NAG Ltd.
! 101: *
! 102: *> \date November 2011
! 103: *
! 104: *> \ingroup doubleOTHERcomputational
! 105: *
! 106: *> \par Further Details:
! 107: * =====================
! 108: *>
! 109: *> \verbatim
! 110: *>
! 111: *> The factorization is obtained by Householder's method. The kth
! 112: *> transformation matrix, Z( k ), which is used to introduce zeros into
! 113: *> the ( m - k + 1 )th row of A, is given in the form
! 114: *>
! 115: *> Z( k ) = ( I 0 ),
! 116: *> ( 0 T( k ) )
! 117: *>
! 118: *> where
! 119: *>
! 120: *> T( k ) = I - tau*u( k )*u( k )**T, u( k ) = ( 1 ),
! 121: *> ( 0 )
! 122: *> ( z( k ) )
! 123: *>
! 124: *> tau is a scalar and z( k ) is an ( n - m ) element vector.
! 125: *> tau and z( k ) are chosen to annihilate the elements of the kth row
! 126: *> of X.
! 127: *>
! 128: *> The scalar tau is returned in the kth element of TAU and the vector
! 129: *> u( k ) in the kth row of A, such that the elements of z( k ) are
! 130: *> in a( k, m + 1 ), ..., a( k, n ). The elements of R are returned in
! 131: *> the upper triangular part of A.
! 132: *>
! 133: *> Z is given by
! 134: *>
! 135: *> Z = Z( 1 ) * Z( 2 ) * ... * Z( m ).
! 136: *> \endverbatim
! 137: *>
! 138: * =====================================================================
1.1 bertrand 139: SUBROUTINE DTZRQF( M, N, A, LDA, TAU, INFO )
140: *
1.10 ! bertrand 141: * -- LAPACK computational routine (version 3.4.0) --
1.1 bertrand 142: * -- LAPACK is a software package provided by Univ. of Tennessee, --
143: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.10 ! bertrand 144: * November 2011
1.1 bertrand 145: *
146: * .. Scalar Arguments ..
147: INTEGER INFO, LDA, M, N
148: * ..
149: * .. Array Arguments ..
150: DOUBLE PRECISION A( LDA, * ), TAU( * )
151: * ..
152: *
153: * =====================================================================
154: *
155: * .. Parameters ..
156: DOUBLE PRECISION ONE, ZERO
157: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
158: * ..
159: * .. Local Scalars ..
160: INTEGER I, K, M1
161: * ..
162: * .. Intrinsic Functions ..
163: INTRINSIC MAX, MIN
164: * ..
165: * .. External Subroutines ..
1.5 bertrand 166: EXTERNAL DAXPY, DCOPY, DGEMV, DGER, DLARFG, XERBLA
1.1 bertrand 167: * ..
168: * .. Executable Statements ..
169: *
170: * Test the input parameters.
171: *
172: INFO = 0
173: IF( M.LT.0 ) THEN
174: INFO = -1
175: ELSE IF( N.LT.M ) THEN
176: INFO = -2
177: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
178: INFO = -4
179: END IF
180: IF( INFO.NE.0 ) THEN
181: CALL XERBLA( 'DTZRQF', -INFO )
182: RETURN
183: END IF
184: *
185: * Perform the factorization.
186: *
187: IF( M.EQ.0 )
188: $ RETURN
189: IF( M.EQ.N ) THEN
190: DO 10 I = 1, N
191: TAU( I ) = ZERO
192: 10 CONTINUE
193: ELSE
194: M1 = MIN( M+1, N )
195: DO 20 K = M, 1, -1
196: *
197: * Use a Householder reflection to zero the kth row of A.
198: * First set up the reflection.
199: *
1.5 bertrand 200: CALL DLARFG( N-M+1, A( K, K ), A( K, M1 ), LDA, TAU( K ) )
1.1 bertrand 201: *
202: IF( ( TAU( K ).NE.ZERO ) .AND. ( K.GT.1 ) ) THEN
203: *
204: * We now perform the operation A := A*P( k ).
205: *
206: * Use the first ( k - 1 ) elements of TAU to store a( k ),
207: * where a( k ) consists of the first ( k - 1 ) elements of
208: * the kth column of A. Also let B denote the first
209: * ( k - 1 ) rows of the last ( n - m ) columns of A.
210: *
211: CALL DCOPY( K-1, A( 1, K ), 1, TAU, 1 )
212: *
213: * Form w = a( k ) + B*z( k ) in TAU.
214: *
215: CALL DGEMV( 'No transpose', K-1, N-M, ONE, A( 1, M1 ),
216: $ LDA, A( K, M1 ), LDA, ONE, TAU, 1 )
217: *
218: * Now form a( k ) := a( k ) - tau*w
1.9 bertrand 219: * and B := B - tau*w*z( k )**T.
1.1 bertrand 220: *
221: CALL DAXPY( K-1, -TAU( K ), TAU, 1, A( 1, K ), 1 )
222: CALL DGER( K-1, N-M, -TAU( K ), TAU, 1, A( K, M1 ), LDA,
223: $ A( 1, M1 ), LDA )
224: END IF
225: 20 CONTINUE
226: END IF
227: *
228: RETURN
229: *
230: * End of DTZRQF
231: *
232: END
CVSweb interface <joel.bertrand@systella.fr>
![[BACK]](/cvsweb/icons/back.gif){kind=icon}
Return to dtzrqf.f CVS log ![[TXT]](/cvsweb/icons/text.gif){kind=icon}
![[DIR]](/cvsweb/icons/dir.gif){kind=icon}
Up to [local] / rpl / lapack / lapack