| // Copyright ©2015 The gonum Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package gonum |
| |
| import ( |
| "gonum.org/v1/gonum/blas" |
| "gonum.org/v1/gonum/lapack" |
| ) |
| |
| // Dgelqf computes the LQ factorization of the m×n matrix A using a blocked |
| // algorithm. See the documentation for Dgelq2 for a description of the |
| // parameters at entry and exit. |
| // |
| // work is temporary storage, and lwork specifies the usable memory length. |
| // At minimum, lwork >= m, and this function will panic otherwise. |
| // Dgelqf is a blocked LQ factorization, but the block size is limited |
| // by the temporary space available. If lwork == -1, instead of performing Dgelqf, |
| // the optimal work length will be stored into work[0]. |
| // |
| // tau must have length at least min(m,n), and this function will panic otherwise. |
| func (impl Implementation) Dgelqf(m, n int, a []float64, lda int, tau, work []float64, lwork int) { |
| nb := impl.Ilaenv(1, "DGELQF", " ", m, n, -1, -1) |
| lworkopt := m * max(nb, 1) |
| if lwork == -1 { |
| work[0] = float64(lworkopt) |
| return |
| } |
| checkMatrix(m, n, a, lda) |
| if len(work) < lwork { |
| panic(shortWork) |
| } |
| if lwork < m { |
| panic(badWork) |
| } |
| k := min(m, n) |
| if len(tau) < k { |
| panic(badTau) |
| } |
| if k == 0 { |
| return |
| } |
| // Find the optimal blocking size based on the size of available memory |
| // and optimal machine parameters. |
| nbmin := 2 |
| var nx int |
| iws := m |
| ldwork := nb |
| if nb > 1 && k > nb { |
| nx = max(0, impl.Ilaenv(3, "DGELQF", " ", m, n, -1, -1)) |
| if nx < k { |
| iws = m * nb |
| if lwork < iws { |
| nb = lwork / m |
| nbmin = max(2, impl.Ilaenv(2, "DGELQF", " ", m, n, -1, -1)) |
| } |
| } |
| } |
| // Computed blocked LQ factorization. |
| var i int |
| if nb >= nbmin && nb < k && nx < k { |
| for i = 0; i < k-nx; i += nb { |
| ib := min(k-i, nb) |
| impl.Dgelq2(ib, n-i, a[i*lda+i:], lda, tau[i:], work) |
| if i+ib < m { |
| impl.Dlarft(lapack.Forward, lapack.RowWise, n-i, ib, |
| a[i*lda+i:], lda, |
| tau[i:], |
| work, ldwork) |
| impl.Dlarfb(blas.Right, blas.NoTrans, lapack.Forward, lapack.RowWise, |
| m-i-ib, n-i, ib, |
| a[i*lda+i:], lda, |
| work, ldwork, |
| a[(i+ib)*lda+i:], lda, |
| work[ib*ldwork:], ldwork) |
| } |
| } |
| } |
| // Perform unblocked LQ factorization on the remainder. |
| if i < k { |
| impl.Dgelq2(m-i, n-i, a[i*lda+i:], lda, tau[i:], work) |
| } |
| } |