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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/blas64"
// Dlaswp swaps the rows k1 to k2 of a rectangular matrix A according to the
// indices in ipiv so that row k is swapped with ipiv[k].
//
// n is the number of columns of A and incX is the increment for ipiv. If incX
// is 1, the swaps are applied from k1 to k2. If incX is -1, the swaps are
// applied in reverse order from k2 to k1. For other values of incX Dlaswp will
// panic. ipiv must have length k2+1, otherwise Dlaswp will panic.
//
// The indices k1, k2, and the elements of ipiv are zero-based.
//
// Dlaswp is an internal routine. It is exported for testing purposes.
func (impl Implementation) Dlaswp(n int, a []float64, lda int, k1, k2 int, ipiv []int, incX int) {
switch {
case n < 0:
panic(nLT0)
case k1 < 0:
panic(badK1)
case k2 < k1:
panic(badK2)
case lda < max(1, n):
panic(badLdA)
case len(a) < k2*lda+n: // A must have at least k2+1 rows.
panic(shortA)
case len(ipiv) != k2+1:
panic(badLenIpiv)
case incX != 1 && incX != -1:
panic(absIncNotOne)
}
if n == 0 {
return
}
bi := blas64.Implementation()
if incX == 1 {
for k := k1; k <= k2; k++ {
if k == ipiv[k] {
continue
}
bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
}
return
}
for k := k2; k >= k1; k-- {
if k == ipiv[k] {
continue
}
bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
}
}
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