// Copyright (C) 2010 Davis E. King (davis@dlib.net)
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_LAPACk_GEQRF_Hh_
#define DLIB_LAPACk_GEQRF_Hh_
#include "fortran_id.h"
#include "../matrix.h"
namespace dlib
{
namespace lapack
{
namespace binding
{
extern "C"
{
void DLIB_FORTRAN_ID(dgeqrf) (integer *m, integer *n, double *a, integer *
lda, double *tau, double *work, integer *lwork,
integer *info);
void DLIB_FORTRAN_ID(sgeqrf) (integer *m, integer *n, float *a, integer *
lda, float *tau, float *work, integer *lwork,
integer *info);
}
inline int geqrf (integer m, integer n, double *a, integer lda,
double *tau, double *work, integer lwork)
{
integer info = 0;
DLIB_FORTRAN_ID(dgeqrf)(&m, &n, a, &lda,
tau, work, &lwork, &info);
return info;
}
inline int geqrf (integer m, integer n, float *a, integer lda,
float *tau, float *work, integer lwork)
{
integer info = 0;
DLIB_FORTRAN_ID(sgeqrf)(&m, &n, a, &lda,
tau, work, &lwork, &info);
return info;
}
}
// ------------------------------------------------------------------------------------
/* -- LAPACK routine (version 3.1) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* DGEQRF computes a QR factorization of a real M-by-N matrix A: */
/* A = Q * R. */
/* Arguments */
/* ========= */
/* M (input) INTEGER */
/* The number of rows of the matrix A. M >= 0. */
/* N (input) INTEGER */
/* The number of columns of the matrix A. N >= 0. */
/* A (input/output) DOUBLE PRECISION array, dimension (LDA,N) */
/* On entry, the M-by-N matrix A. */
/* On exit, the elements on and above the diagonal of the array */
/* contain the min(M,N)-by-N upper trapezoidal matrix R (R is */
/* upper triangular if m >= n); the elements below the diagonal, */
/* with the array TAU, represent the orthogonal matrix Q as a */
/* product of min(m,n) elementary reflectors (see Further */
/* Details). */
/* LDA (input) INTEGER */
/* The leading dimension of the array A. LDA >= max(1,M). */
/* TAU (output) DOUBLE PRECISION array, dimension (min(M,N)) */
/* The scalar factors of the elementary reflectors (see Further */
/* Details). */
/* WORK (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK)) */
/* On exit, if INFO = 0, WORK(1) returns the optimal LWORK. */
/* LWORK (input) INTEGER */
/* The dimension of the array WORK. LWORK >= max(1,N). */
/* For optimum performance LWORK >= N*NB, where NB is */
/* the optimal blocksize. */
/* If LWORK = -1, then a workspace query is assumed; the routine */
/* only calculates the optimal size of the WORK array, returns */
/* this value as the first entry of the WORK array, and no error */
/* message related to LWORK is issued by XERBLA. */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* Further Details */
/* =============== */
/* The matrix Q is represented as a product of elementary reflectors */
/* Q = H(1) H(2) . . . H(k), where k = min(m,n). */
/* Each H(i) has the form */
/* H(i) = I - tau * v * v' */
/* 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), */
/* and tau in TAU(i). */
// ------------------------------------------------------------------------------------
template <
typename T,
long NR1, long NR2,
long NC1, long NC2,
typename MM
>
int geqrf (
matrix<T,NR1,NC1,MM,column_major_layout>& a,
matrix<T,NR2,NC2,MM,column_major_layout>& tau
)
{
matrix<T,0,1,MM,column_major_layout> work;
tau.set_size(std::min(a.nr(), a.nc()), 1);
// figure out how big the workspace needs to be.
T work_size = 1;
int info = binding::geqrf(a.nr(), a.nc(), &a(0,0), a.nr(),
&tau(0,0), &work_size, -1);
if (info != 0)
return info;
if (work.size() < work_size)
work.set_size(static_cast<long>(work_size), 1);
// compute the actual decomposition
info = binding::geqrf(a.nr(), a.nc(), &a(0,0), a.nr(),
&tau(0,0), &work(0,0), work.size());
return info;
}
// ------------------------------------------------------------------------------------
}
}
// ----------------------------------------------------------------------------------------
#endif // DLIB_LAPACk_GEQRF_Hh_