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ec100cf00f
Improved function documentation Fixed dlarfb and dlarft and added full tests Added dgelq2 Working Dgels Fix many comments and tests Many PR comment responses Responded to more PR comments Many PR comments
83 lines
2.2 KiB
Go
83 lines
2.2 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 native
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import (
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"github.com/gonum/blas"
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"github.com/gonum/blas/blas64"
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)
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// Dlarf applies an elementary reflector to a general rectangular matrix c.
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// This computes
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// c = h * c if side == Left
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// c = c * h if side == right
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// where
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// h = 1 - tau * v * v^T
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// and c is an m * n matrix.
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//
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// Work is temporary storage of length at least m if side == Left and at least
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// n if side == Right. This function will panic if this length requirement is not met.
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func (impl Implementation) Dlarf(side blas.Side, m, n int, v []float64, incv int, tau float64, c []float64, ldc int, work []float64) {
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applyleft := side == blas.Left
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if (applyleft && len(work) < n) || (!applyleft && len(work) < m) {
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panic(badWork)
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}
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checkMatrix(m, n, c, ldc)
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// v has length m if applyleft and n otherwise.
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lenV := n
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if applyleft {
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lenV = m
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}
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checkVector(lenV, v, incv)
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lastv := 0 // last non-zero element of v
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lastc := 0 // last non-zero row/column of c
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if tau != 0 {
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var i int
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if applyleft {
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lastv = m - 1
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} else {
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lastv = n - 1
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}
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if incv > 0 {
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i = lastv * incv
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}
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// Look for the last non-zero row in v.
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for lastv >= 0 && v[i] == 0 {
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lastv--
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i -= incv
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}
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if applyleft {
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// Scan for the last non-zero column in C[0:lastv, :]
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lastc = impl.Iladlc(lastv+1, n, c, ldc)
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} else {
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// Scan for the last non-zero row in C[:, 0:lastv]
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lastc = impl.Iladlr(m, lastv+1, c, ldc)
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}
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}
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if lastv == -1 || lastc == -1 {
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return
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}
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// Sometimes 1-indexing is nicer ...
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bi := blas64.Implementation()
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if applyleft {
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// Form H * C
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// w[0:lastc+1] = c[1:lastv+1, 1:lastc+1]^T * v[1:lastv+1,1]
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bi.Dgemv(blas.Trans, lastv+1, lastc+1, 1, c, ldc, v, incv, 0, work, 1)
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// c[0: lastv, 0: lastc] = c[...] - w[0:lastv, 1] * v[1:lastc, 1]^T
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bi.Dger(lastv+1, lastc+1, -tau, v, incv, work, 1, c, ldc)
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return
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}
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// Form C*H
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// w[0:lastc+1,1] := c[0:lastc+1,0:lastv+1] * v[0:lastv+1,1]
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bi.Dgemv(blas.NoTrans, lastc+1, lastv+1, 1, c, ldc, v, incv, 0, work, 1)
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// c[0:lastc+1,0:lastv+1] = c[...] - w[0:lastc+1,0] * v[0:lastv+1,0]^T
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bi.Dger(lastc+1, lastv+1, -tau, work, 1, v, incv, c, ldc)
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}
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