| // 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" |
| ) |
| |
| // Dgeqrf computes the QR factorization of the m×n matrix A using a blocked |
| // algorithm. See the documentation for Dgeqr2 for a description of the |
| // parameters at entry and exit. |
| // |
| // work is temporary storage, and lwork specifies the usable memory length. |
| // The length of work must be at least max(1, lwork) and lwork must be -1 |
| // or at least n, otherwise this function will panic. |
| // Dgeqrf is a blocked QR factorization, but the block size is limited |
| // by the temporary space available. If lwork == -1, instead of performing Dgeqrf, |
| // 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) Dgeqrf(m, n int, a []float64, lda int, tau, work []float64, lwork int) { |
| if len(work) < max(1, lwork) { |
| panic(shortWork) |
| } |
| // nb is the optimal blocksize, i.e. the number of columns transformed at a time. |
| nb := impl.Ilaenv(1, "DGEQRF", " ", m, n, -1, -1) |
| lworkopt := n * max(nb, 1) |
| lworkopt = max(n, lworkopt) |
| if lwork == -1 { |
| work[0] = float64(lworkopt) |
| return |
| } |
| checkMatrix(m, n, a, lda) |
| if lwork < n { |
| panic(badWork) |
| } |
| k := min(m, n) |
| if len(tau) < k { |
| panic(badTau) |
| } |
| if k == 0 { |
| work[0] = float64(lworkopt) |
| return |
| } |
| nbmin := 2 // Minimal block size. |
| var nx int // Use unblocked (unless changed in the next for loop) |
| iws := n |
| ldwork := nb |
| // Only consider blocked if the suggested block size is > 1 and the |
| // number of rows or columns is sufficiently large. |
| if 1 < nb && nb < k { |
| // nx is the block size at which the code switches from blocked |
| // to unblocked. |
| nx = max(0, impl.Ilaenv(3, "DGEQRF", " ", m, n, -1, -1)) |
| if k > nx { |
| iws = ldwork * n |
| if lwork < iws { |
| // Not enough workspace to use the optimal block |
| // size. Get the minimum block size instead. |
| nb = lwork / n |
| nbmin = max(2, impl.Ilaenv(2, "DGEQRF", " ", m, n, -1, -1)) |
| } |
| } |
| } |
| for i := range work { |
| work[i] = 0 |
| } |
| // Compute QR using a blocked algorithm. |
| var i int |
| if nbmin <= nb && nb < k && nx < k { |
| for i = 0; i < k-nx; i += nb { |
| ib := min(k-i, nb) |
| // Compute the QR factorization of the current block. |
| impl.Dgeqr2(m-i, ib, a[i*lda+i:], lda, tau[i:], work) |
| if i+ib < n { |
| // Form the triangular factor of the block reflector and apply H^T |
| // In Dlarft, work becomes the T matrix. |
| impl.Dlarft(lapack.Forward, lapack.ColumnWise, m-i, ib, |
| a[i*lda+i:], lda, |
| tau[i:], |
| work, ldwork) |
| impl.Dlarfb(blas.Left, blas.Trans, lapack.Forward, lapack.ColumnWise, |
| m-i, n-i-ib, ib, |
| a[i*lda+i:], lda, |
| work, ldwork, |
| a[i*lda+i+ib:], lda, |
| work[ib*ldwork:], ldwork) |
| } |
| } |
| } |
| // Call unblocked code on the remaining columns. |
| if i < k { |
| impl.Dgeqr2(m-i, n-i, a[i*lda+i:], lda, tau[i:], work) |
| } |
| work[0] = float64(lworkopt) |
| } |