89 lines
1.6 KiB
Go
89 lines
1.6 KiB
Go
// Copyright ©2022 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 "gonum.org/v1/gonum/blas/blas64"
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// Dlapmr rearranges the rows of the m×n matrix X as specified by the permutation
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// k[0],k[1],...,k[m-1] of the integers 0,...,m-1.
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//
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// If forward is true, a forward permutation is applied:
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//
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// X[k[i],0:n] is moved to X[i,0:n] for i=0,1,...,m-1.
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//
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// If forward is false, a backward permutation is applied:
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//
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// X[i,0:n] is moved to X[k[i],0:n] for i=0,1,...,m-1.
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//
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// k must have length m, otherwise Dlapmr will panic.
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func (impl Implementation) Dlapmr(forward bool, m, n int, x []float64, ldx int, k []int) {
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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 ldx < max(1, n):
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panic(badLdX)
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}
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// Quick return if possible.
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if m == 0 || n == 0 {
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return
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}
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switch {
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case len(x) < (m-1)*ldx+n:
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panic(shortX)
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case len(k) != m:
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panic(badLenK)
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}
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// Quick return if possible.
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if m == 1 {
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return
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}
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bi := blas64.Implementation()
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for i, ki := range k {
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k[i] = -(ki + 1)
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}
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if forward {
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for i, ki := range k {
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if ki >= 0 {
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continue
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}
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j := i
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k[j] = -k[j] - 1
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in := k[j]
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for {
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if k[in] >= 0 {
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break
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}
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bi.Dswap(n, x[j*ldx:], 1, x[in*ldx:], 1)
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k[in] = -k[in] - 1
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j = in
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in = k[in]
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}
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}
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} else {
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for i, ki := range k {
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if ki >= 0 {
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continue
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}
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k[i] = -ki - 1
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j := k[i]
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for {
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if j == i {
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break
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}
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bi.Dswap(n, x[i*ldx:], 1, x[j*ldx:], 1)
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k[j] = -k[j] - 1
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j = k[j]
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}
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}
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}
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}
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