| // Copyright ©2020 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 distmat |
| |
| import ( |
| "golang.org/x/exp/rand" |
| |
| "gonum.org/v1/gonum/mat" |
| ) |
| |
| // UniformPermutation is a uniform distribution over the n! |
| // permutation matrices of size n×n for a given n. |
| type UniformPermutation struct { |
| rnd *rand.Rand |
| indices []int |
| } |
| |
| // NewUniformPermutation constructs a new permutation matrix |
| // generator using the given random source. |
| func NewUniformPermutation(src rand.Source) *UniformPermutation { |
| return &UniformPermutation{rnd: rand.New(src)} |
| } |
| |
| // PermTo sets the given matrix to be a random permutation matrix. |
| // It does not zero the destination's elements, so it is the responsibility |
| // of the caller to ensure it is correctly conditioned prior to the call. |
| // |
| // PermTo panics if dst is not square. |
| func (p *UniformPermutation) PermTo(dst *mat.Dense) { |
| r, c := dst.Dims() |
| if r != c { |
| panic(mat.ErrShape) |
| } |
| if r == 0 { |
| return |
| } |
| if len(p.indices) != r { |
| p.indices = make([]int, r) |
| for k := range p.indices { |
| p.indices[k] = k |
| } |
| } |
| p.rnd.Shuffle(r, func(i, j int) { p.indices[i], p.indices[j] = p.indices[j], p.indices[i] }) |
| for i, j := range p.indices { |
| dst.Set(i, j, 1) |
| } |
| } |