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// Copyright ©2022 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/blas64"
// Dlapmr rearranges the rows of the m×n matrix X as specified by the permutation
// k[0],k[1],...,k[m-1] of the integers 0,...,m-1.
//
// If forward is true, a forward permutation is applied:
//
// X[k[i],0:n] is moved to X[i,0:n] for i=0,1,...,m-1.
//
// If forward is false, a backward permutation is applied:
//
// X[i,0:n] is moved to X[k[i],0:n] for i=0,1,...,m-1.
//
// k must have length m, otherwise Dlapmr will panic.
func (impl Implementation) Dlapmr(forward bool, m, n int, x []float64, ldx int, k []int) {
switch {
case m < 0:
panic(mLT0)
case n < 0:
panic(nLT0)
case ldx < max(1, n):
panic(badLdX)
}
// Quick return if possible.
if m == 0 || n == 0 {
return
}
switch {
case len(x) < (m-1)*ldx+n:
panic(shortX)
case len(k) != m:
panic(badLenK)
}
// Quick return if possible.
if m == 1 {
return
}
bi := blas64.Implementation()
for i, ki := range k {
k[i] = -(ki + 1)
}
if forward {
for i, ki := range k {
if ki >= 0 {
continue
}
j := i
k[j] = -k[j] - 1
in := k[j]
for {
if k[in] >= 0 {
break
}
bi.Dswap(n, x[j*ldx:], 1, x[in*ldx:], 1)
k[in] = -k[in] - 1
j = in
in = k[in]
}
}
} else {
for i, ki := range k {
if ki >= 0 {
continue
}
k[i] = -ki - 1
j := k[i]
for {
if j == i {
break
}
bi.Dswap(n, x[i*ldx:], 1, x[j*ldx:], 1)
k[j] = -k[j] - 1
j = k[j]
}
}
}
}
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