*> \brief \b DGEQPF * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download DGEQPF + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * SUBROUTINE DGEQPF( M, N, A, LDA, JPVT, TAU, WORK, INFO ) * * .. Scalar Arguments .. * INTEGER INFO, LDA, M, N * .. * .. Array Arguments .. * INTEGER JPVT( * ) * DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> This routine is deprecated and has been replaced by routine DGEQP3. *> *> DGEQPF computes a QR factorization with column pivoting of a *> real M-by-N matrix A: A*P = Q*R. *> \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 >= 0 *> \endverbatim *> *> \param[in,out] A *> \verbatim *> A is DOUBLE PRECISION array, dimension (LDA,N) *> On entry, the M-by-N matrix A. *> On exit, the upper triangle of the array contains the *> min(M,N)-by-N upper triangular matrix R; the elements *> below the diagonal, together with the array TAU, *> represent the orthogonal matrix Q as a product of *> min(m,n) elementary reflectors. *> \endverbatim *> *> \param[in] LDA *> \verbatim *> LDA is INTEGER *> The leading dimension of the array A. LDA >= max(1,M). *> \endverbatim *> *> \param[in,out] JPVT *> \verbatim *> JPVT is INTEGER array, dimension (N) *> On entry, if JPVT(i) .ne. 0, the i-th column of A is permuted *> to the front of A*P (a leading column); if JPVT(i) = 0, *> the i-th column of A is a free column. *> On exit, if JPVT(i) = k, then the i-th column of A*P *> was the k-th column of A. *> \endverbatim *> *> \param[out] TAU *> \verbatim *> TAU is DOUBLE PRECISION array, dimension (min(M,N)) *> The scalar factors of the elementary reflectors. *> \endverbatim *> *> \param[out] WORK *> \verbatim *> WORK is DOUBLE PRECISION array, dimension (3*N) *> \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 doubleGEcomputational * *> \par Further Details: * ===================== *> *> \verbatim *> *> The matrix Q is represented as a product of elementary reflectors *> *> Q = H(1) H(2) . . . H(n) *> *> Each H(i) has the form *> *> H = I - tau * v * v**T *> *> where tau is a real scalar, and v is a real vector with *> v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i). *> *> The matrix P is represented in jpvt as follows: If *> jpvt(j) = i *> then the jth column of P is the ith canonical unit vector. *> *> Partial column norm updating strategy modified by *> Z. Drmac and Z. Bujanovic, Dept. of Mathematics, *> University of Zagreb, Croatia. *> -- April 2011 -- *> For more details see LAPACK Working Note 176. *> \endverbatim *> * ===================================================================== SUBROUTINE DGEQPF( M, N, A, LDA, JPVT, TAU, WORK, 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 .. INTEGER JPVT( * ) DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * ) * .. * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ZERO, ONE PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 ) * .. * .. Local Scalars .. INTEGER I, ITEMP, J, MA, MN, PVT DOUBLE PRECISION AII, TEMP, TEMP2, TOL3Z * .. * .. External Subroutines .. EXTERNAL DGEQR2, DLARF, DLARFG, DORM2R, DSWAP, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC ABS, MAX, MIN, SQRT * .. * .. External Functions .. INTEGER IDAMAX DOUBLE PRECISION DLAMCH, DNRM2 EXTERNAL IDAMAX, DLAMCH, DNRM2 * .. * .. Executable Statements .. * * Test the input arguments * INFO = 0 IF( M.LT.0 ) THEN INFO = -1 ELSE IF( N.LT.0 ) THEN INFO = -2 ELSE IF( LDA.LT.MAX( 1, M ) ) THEN INFO = -4 END IF IF( INFO.NE.0 ) THEN CALL XERBLA( 'DGEQPF', -INFO ) RETURN END IF * MN = MIN( M, N ) TOL3Z = SQRT(DLAMCH('Epsilon')) * * Move initial columns up front * ITEMP = 1 DO 10 I = 1, N IF( JPVT( I ).NE.0 ) THEN IF( I.NE.ITEMP ) THEN CALL DSWAP( M, A( 1, I ), 1, A( 1, ITEMP ), 1 ) JPVT( I ) = JPVT( ITEMP ) JPVT( ITEMP ) = I ELSE JPVT( I ) = I END IF ITEMP = ITEMP + 1 ELSE JPVT( I ) = I END IF 10 CONTINUE ITEMP = ITEMP - 1 * * Compute the QR factorization and update remaining columns * IF( ITEMP.GT.0 ) THEN MA = MIN( ITEMP, M ) CALL DGEQR2( M, MA, A, LDA, TAU, WORK, INFO ) IF( MA.LT.N ) THEN CALL DORM2R( 'Left', 'Transpose', M, N-MA, MA, A, LDA, TAU, \$ A( 1, MA+1 ), LDA, WORK, INFO ) END IF END IF * IF( ITEMP.LT.MN ) THEN * * Initialize partial column norms. The first n elements of * work store the exact column norms. * DO 20 I = ITEMP + 1, N WORK( I ) = DNRM2( M-ITEMP, A( ITEMP+1, I ), 1 ) WORK( N+I ) = WORK( I ) 20 CONTINUE * * Compute factorization * DO 40 I = ITEMP + 1, MN * * Determine ith pivot column and swap if necessary * PVT = ( I-1 ) + IDAMAX( N-I+1, WORK( I ), 1 ) * IF( PVT.NE.I ) THEN CALL DSWAP( M, A( 1, PVT ), 1, A( 1, I ), 1 ) ITEMP = JPVT( PVT ) JPVT( PVT ) = JPVT( I ) JPVT( I ) = ITEMP WORK( PVT ) = WORK( I ) WORK( N+PVT ) = WORK( N+I ) END IF * * Generate elementary reflector H(i) * IF( I.LT.M ) THEN CALL DLARFG( M-I+1, A( I, I ), A( I+1, I ), 1, TAU( I ) ) ELSE CALL DLARFG( 1, A( M, M ), A( M, M ), 1, TAU( M ) ) END IF * IF( I.LT.N ) THEN * * Apply H(i) to A(i:m,i+1:n) from the left * AII = A( I, I ) A( I, I ) = ONE CALL DLARF( 'LEFT', M-I+1, N-I, A( I, I ), 1, TAU( I ), \$ A( I, I+1 ), LDA, WORK( 2*N+1 ) ) A( I, I ) = AII END IF * * Update partial column norms * DO 30 J = I + 1, N IF( WORK( J ).NE.ZERO ) THEN * * NOTE: The following 4 lines follow from the analysis in * Lapack Working Note 176. * TEMP = ABS( A( I, J ) ) / WORK( J ) TEMP = MAX( ZERO, ( ONE+TEMP )*( ONE-TEMP ) ) TEMP2 = TEMP*( WORK( J ) / WORK( N+J ) )**2 IF( TEMP2 .LE. TOL3Z ) THEN IF( M-I.GT.0 ) THEN WORK( J ) = DNRM2( M-I, A( I+1, J ), 1 ) WORK( N+J ) = WORK( J ) ELSE WORK( J ) = ZERO WORK( N+J ) = ZERO END IF ELSE WORK( J ) = WORK( J )*SQRT( TEMP ) END IF END IF 30 CONTINUE * 40 CONTINUE END IF RETURN * * End of DGEQPF * END