*> \brief \b STZRQF * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download STZRQF + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE STZRQF( M, N, A, LDA, TAU, INFO ) * * .. Scalar Arguments .. * INTEGER INFO, LDA, M, N * .. * .. Array Arguments .. * REAL A( LDA, * ), TAU( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> This routine is deprecated and has been replaced by routine STZRZF. *> *> STZRQF reduces the M-by-N ( M<=N ) real upper trapezoidal matrix A *> to upper triangular form by means of orthogonal transformations. *> *> The upper trapezoidal matrix A is factored as *> *> A = ( R 0 ) * Z, *> *> where Z is an N-by-N orthogonal matrix and R is an M-by-M upper *> triangular matrix. *> \endverbatim * * Arguments: * ========== * *> \param[in] M *> \verbatim *> M is INTEGER *> The number of rows of the matrix A. M >= 0. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> The number of columns of the matrix A. N >= M. *> \endverbatim *> *> \param[in,out] A *> \verbatim *> A is REAL array, dimension (LDA,N) *> On entry, the leading M-by-N upper trapezoidal part of the *> array A must contain the matrix to be factorized. *> On exit, the leading M-by-M upper triangular part of A *> contains the upper triangular matrix R, and elements M+1 to *> N of the first M rows of A, with the array TAU, represent the *> orthogonal matrix Z as a product of M elementary reflectors. *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> The leading dimension of the array A. LDA >= max(1,M). *> \endverbatim *> *> \param[out] TAU *> \verbatim *> TAU is REAL array, dimension (M) *> The scalar factors of the elementary reflectors. *> \endverbatim *> *> \param[out] INFO *> \verbatim *> INFO is INTEGER *> = 0: successful exit *> < 0: if INFO = -i, the i-th argument had an illegal value *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date November 2011 * *> \ingroup realOTHERcomputational * *> \par Further Details: * ===================== *> *> \verbatim *> *> The factorization is obtained by Householder's method. The kth *> transformation matrix, Z( k ), which is used to introduce zeros into *> the ( m - k + 1 )th row of A, is given in the form *> *> Z( k ) = ( I 0 ), *> ( 0 T( k ) ) *> *> where *> *> T( k ) = I - tau*u( k )*u( k )**T, u( k ) = ( 1 ), *> ( 0 ) *> ( z( k ) ) *> *> tau is a scalar and z( k ) is an ( n - m ) element vector. *> tau and z( k ) are chosen to annihilate the elements of the kth row *> of X. *> *> The scalar tau is returned in the kth element of TAU and the vector *> u( k ) in the kth row of A, such that the elements of z( k ) are *> in a( k, m + 1 ), ..., a( k, n ). The elements of R are returned in *> the upper triangular part of A. *> *> Z is given by *> *> Z = Z( 1 ) * Z( 2 ) * ... * Z( m ). *> \endverbatim *> * ===================================================================== SUBROUTINE STZRQF( M, N, A, LDA, TAU, INFO ) * * -- LAPACK computational routine (version 3.4.0) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2011 * * .. Scalar Arguments .. INTEGER INFO, LDA, M, N * .. * .. Array Arguments .. REAL A( LDA, * ), TAU( * ) * .. * * ===================================================================== * * .. Parameters .. REAL ONE, ZERO PARAMETER ( ONE = 1.0E+0, ZERO = 0.0E+0 ) * .. * .. Local Scalars .. INTEGER I, K, M1 * .. * .. Intrinsic Functions .. INTRINSIC MAX, MIN * .. * .. External Subroutines .. EXTERNAL SAXPY, SCOPY, SGEMV, SGER, SLARFG, XERBLA * .. * .. Executable Statements .. * * Test the input parameters. * INFO = 0 IF( M.LT.0 ) THEN INFO = -1 ELSE IF( N.LT.M ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN INFO = -4 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'STZRQF', -INFO ) RETURN END IF * * Perform the factorization. * IF( M.EQ.0 ) \$ RETURN IF( M.EQ.N ) THEN DO 10 I = 1, N TAU( I ) = ZERO 10 CONTINUE ELSE M1 = MIN( M+1, N ) DO 20 K = M, 1, -1 * * Use a Householder reflection to zero the kth row of A. * First set up the reflection. * CALL SLARFG( N-M+1, A( K, K ), A( K, M1 ), LDA, TAU( K ) ) * IF( ( TAU( K ).NE.ZERO ) .AND. ( K.GT.1 ) ) THEN * * We now perform the operation A := A*P( k ). * * Use the first ( k - 1 ) elements of TAU to store a( k ), * where a( k ) consists of the first ( k - 1 ) elements of * the kth column of A. Also let B denote the first * ( k - 1 ) rows of the last ( n - m ) columns of A. * CALL SCOPY( K-1, A( 1, K ), 1, TAU, 1 ) * * Form w = a( k ) + B*z( k ) in TAU. * CALL SGEMV( 'No transpose', K-1, N-M, ONE, A( 1, M1 ), \$ LDA, A( K, M1 ), LDA, ONE, TAU, 1 ) * * Now form a( k ) := a( k ) - tau*w * and B := B - tau*w*z( k )**T. * CALL SAXPY( K-1, -TAU( K ), TAU, 1, A( 1, K ), 1 ) CALL SGER( K-1, N-M, -TAU( K ), TAU, 1, A( K, M1 ), LDA, \$ A( 1, M1 ), LDA ) END IF 20 CONTINUE END IF * RETURN * * End of STZRQF * END