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78 lines
1.6 KiB
Go
78 lines
1.6 KiB
Go
// Copyright ©2015 The Gonum Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package gonum
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import (
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"gonum.org/v1/gonum/blas"
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"gonum.org/v1/gonum/blas/blas64"
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)
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// Dorg2r generates an m×n matrix Q with orthonormal columns defined by the
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// product of elementary reflectors as computed by Dgeqrf.
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//
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// Q = H_0 * H_1 * ... * H_{k-1}
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//
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// len(tau) = k, 0 <= k <= n, 0 <= n <= m, len(work) >= n.
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// Dorg2r will panic if these conditions are not met.
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//
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// Dorg2r is an internal routine. It is exported for testing purposes.
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func (impl Implementation) Dorg2r(m, n, k int, a []float64, lda int, tau []float64, work []float64) {
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switch {
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case m < 0:
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panic(mLT0)
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case n < 0:
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panic(nLT0)
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case n > m:
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panic(nGTM)
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case k < 0:
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panic(kLT0)
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case k > n:
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panic(kGTN)
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case lda < max(1, n):
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panic(badLdA)
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}
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if n == 0 {
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return
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}
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switch {
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case len(a) < (m-1)*lda+n:
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panic(shortA)
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case len(tau) != k:
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panic(badLenTau)
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case len(work) < n:
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panic(shortWork)
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}
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bi := blas64.Implementation()
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// Initialize columns k+1:n to columns of the unit matrix.
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for l := 0; l < m; l++ {
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for j := k; j < n; j++ {
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a[l*lda+j] = 0
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}
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}
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for j := k; j < n; j++ {
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a[j*lda+j] = 1
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}
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for i := k - 1; i >= 0; i-- {
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for i := range work {
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work[i] = 0
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}
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if i < n-1 {
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a[i*lda+i] = 1
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impl.Dlarf(blas.Left, m-i, n-i-1, a[i*lda+i:], lda, tau[i], a[i*lda+i+1:], lda, work)
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}
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if i < m-1 {
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bi.Dscal(m-i-1, -tau[i], a[(i+1)*lda+i:], lda)
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}
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a[i*lda+i] = 1 - tau[i]
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for l := 0; l < i; l++ {
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a[l*lda+i] = 0
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}
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}
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}
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