59 lines
1.5 KiB
Go
59 lines
1.5 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 "gonum.org/v1/gonum/blas/blas64"
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// Dlaswp swaps the rows k1 to k2 of a rectangular matrix A according to the
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// indices in ipiv so that row k is swapped with ipiv[k].
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//
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// n is the number of columns of A and incX is the increment for ipiv. If incX
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// is 1, the swaps are applied from k1 to k2. If incX is -1, the swaps are
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// applied in reverse order from k2 to k1. For other values of incX Dlaswp will
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// panic. ipiv must have length k2+1, otherwise Dlaswp will panic.
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//
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// The indices k1, k2, and the elements of ipiv are zero-based.
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//
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// Dlaswp is an internal routine. It is exported for testing purposes.
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func (impl Implementation) Dlaswp(n int, a []float64, lda int, k1, k2 int, ipiv []int, incX int) {
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switch {
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case n < 0:
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panic(nLT0)
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case k1 < 0:
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panic(badK1)
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case k2 < k1:
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panic(badK2)
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case lda < max(1, n):
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panic(badLdA)
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case len(a) < k2*lda+n: // A must have at least k2+1 rows.
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panic(shortA)
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case len(ipiv) != k2+1:
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panic(badLenIpiv)
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case incX != 1 && incX != -1:
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panic(absIncNotOne)
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}
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if n == 0 {
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return
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}
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bi := blas64.Implementation()
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if incX == 1 {
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for k := k1; k <= k2; k++ {
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if k == ipiv[k] {
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continue
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}
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bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
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}
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return
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}
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for k := k2; k >= k1; k-- {
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if k == ipiv[k] {
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continue
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}
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bi.Dswap(n, a[k*lda:], 1, a[ipiv[k]*lda:], 1)
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}
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}
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