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// 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"
)
// Dormlq multiplies the matrix C by the orthogonal matrix Q defined by the
// slices a and tau. A and tau are as returned from Dgelqf.
//
// C = Q * C if side == blas.Left and trans == blas.NoTrans
// C = Qᵀ * C if side == blas.Left and trans == blas.Trans
// C = C * Q if side == blas.Right and trans == blas.NoTrans
// C = C * Qᵀ if side == blas.Right and trans == blas.Trans
//
// If side == blas.Left, A is a matrix of side k×m, and if side == blas.Right
// A is of size k×n. This uses a blocked algorithm.
//
// work is temporary storage, and lwork specifies the usable memory length.
// At minimum, lwork >= m if side == blas.Left and lwork >= n if side == blas.Right,
// and this function will panic otherwise.
// Dormlq uses a block algorithm, but the block size is limited
// by the temporary space available. If lwork == -1, instead of performing Dormlq,
// the optimal work length will be stored into work[0].
//
// tau contains the Householder scales and must have length at least k, and
// this function will panic otherwise.
func (impl Implementation) Dormlq(side blas.Side, trans blas.Transpose, m, n, k int, a []float64, lda int, tau, c []float64, ldc int, work []float64, lwork int) {
left := side == blas.Left
nw := m
if left {
nw = n
}
switch {
case !left && side != blas.Right:
panic(badSide)
case trans != blas.Trans && trans != blas.NoTrans:
panic(badTrans)
case m < 0:
panic(mLT0)
case n < 0:
panic(nLT0)
case k < 0:
panic(kLT0)
case left && k > m:
panic(kGTM)
case !left && k > n:
panic(kGTN)
case left && lda < max(1, m):
panic(badLdA)
case !left && lda < max(1, n):
panic(badLdA)
case lwork < max(1, nw) && lwork != -1:
panic(badLWork)
case len(work) < max(1, lwork):
panic(shortWork)
}
// Quick return if possible.
if m == 0 || n == 0 || k == 0 {
work[0] = 1
return
}
const (
nbmax = 64
ldt = nbmax
tsize = nbmax * ldt
)
opts := string(side) + string(trans)
nb := min(nbmax, impl.Ilaenv(1, "DORMLQ", opts, m, n, k, -1))
lworkopt := max(1, nw)*nb + tsize
if lwork == -1 {
work[0] = float64(lworkopt)
return
}
switch {
case left && len(a) < (k-1)*lda+m:
panic(shortA)
case !left && len(a) < (k-1)*lda+n:
panic(shortA)
case len(tau) < k:
panic(shortTau)
case len(c) < (m-1)*ldc+n:
panic(shortC)
}
nbmin := 2
if 1 < nb && nb < k {
iws := nw*nb + tsize
if lwork < iws {
nb = (lwork - tsize) / nw
nbmin = max(2, impl.Ilaenv(2, "DORMLQ", opts, m, n, k, -1))
}
}
if nb < nbmin || k <= nb {
// Call unblocked code.
impl.Dorml2(side, trans, m, n, k, a, lda, tau, c, ldc, work)
work[0] = float64(lworkopt)
return
}
t := work[:tsize]
wrk := work[tsize:]
ldwrk := nb
notrans := trans == blas.NoTrans
transt := blas.NoTrans
if notrans {
transt = blas.Trans
}
switch {
case left && notrans:
for i := 0; i < k; i += nb {
ib := min(nb, k-i)
impl.Dlarft(lapack.Forward, lapack.RowWise, m-i, ib,
a[i*lda+i:], lda,
tau[i:],
t, ldt)
impl.Dlarfb(side, transt, lapack.Forward, lapack.RowWise, m-i, n, ib,
a[i*lda+i:], lda,
t, ldt,
c[i*ldc:], ldc,
wrk, ldwrk)
}
case left && !notrans:
for i := ((k - 1) / nb) * nb; i >= 0; i -= nb {
ib := min(nb, k-i)
impl.Dlarft(lapack.Forward, lapack.RowWise, m-i, ib,
a[i*lda+i:], lda,
tau[i:],
t, ldt)
impl.Dlarfb(side, transt, lapack.Forward, lapack.RowWise, m-i, n, ib,
a[i*lda+i:], lda,
t, ldt,
c[i*ldc:], ldc,
wrk, ldwrk)
}
case !left && notrans:
for i := ((k - 1) / nb) * nb; i >= 0; i -= nb {
ib := min(nb, k-i)
impl.Dlarft(lapack.Forward, lapack.RowWise, n-i, ib,
a[i*lda+i:], lda,
tau[i:],
t, ldt)
impl.Dlarfb(side, transt, lapack.Forward, lapack.RowWise, m, n-i, ib,
a[i*lda+i:], lda,
t, ldt,
c[i:], ldc,
wrk, ldwrk)
}
case !left && !notrans:
for i := 0; i < k; i += nb {
ib := min(nb, k-i)
impl.Dlarft(lapack.Forward, lapack.RowWise, n-i, ib,
a[i*lda+i:], lda,
tau[i:],
t, ldt)
impl.Dlarfb(side, transt, lapack.Forward, lapack.RowWise, m, n-i, ib,
a[i*lda+i:], lda,
t, ldt,
c[i:], ldc,
wrk, ldwrk)
}
}
work[0] = float64(lworkopt)
}
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