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 // Copyright ©2017 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" // Dlapmt rearranges the columns of the m×n matrix X as specified by the // permutation k_0, k_1, ..., k_n-1 of the integers 0, ..., n-1. // // If forward is true a forward permutation is performed: // // X[0:m, k[j]] is moved to X[0:m, j] for j = 0, 1, ..., n-1. // // otherwise a backward permutation is performed: // // X[0:m, j] is moved to X[0:m, k[j]] for j = 0, 1, ..., n-1. // // k must have length n, otherwise Dlapmt will panic. k is zero-indexed. func (impl Implementation) Dlapmt(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) != n: panic(badLenK) } // Quick return if possible. if n == 1 { return } for i, v := range k { v++ k[i] = -v } bi := blas64.Implementation() if forward { for j, v := range k { if v >= 0 { continue } k[j] = -v i := -v - 1 for k[i] < 0 { bi.Dswap(m, x[j:], ldx, x[i:], ldx) k[i] = -k[i] j = i i = k[i] - 1 } } } else { for i, v := range k { if v >= 0 { continue } k[i] = -v j := -v - 1 for j != i { bi.Dswap(m, x[j:], ldx, x[i:], ldx) k[j] = -k[j] j = k[j] - 1 } } } for i := range k { k[i]-- } }