| // 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" |
| "gonum.org/v1/gonum/stat/distuv" |
| ) |
| |
| // UnitVector is a uniform distribution over the surface of a sphere. |
| type UnitVector struct { |
| norm distuv.Normal |
| } |
| |
| // NewUnitVector constructs a unit vector generator. |
| func NewUnitVector(src rand.Source) *UnitVector { |
| return &UnitVector{norm: distuv.Normal{Mu: 0, Sigma: 1, Src: src}} |
| } |
| |
| // UnitVecTo sets dst to be a random unit-length vector. |
| // |
| // This uses the algorithm of Mueller from: |
| // https://dl.acm.org/doi/10.1145/377939.377946 |
| // and summarized at: |
| // https://mathworld.wolfram.com/HyperspherePointPicking.html |
| // |
| // UnitVecTo panics if dst has 0 length. |
| func (u *UnitVector) UnitVecTo(dst *mat.VecDense) { |
| r := dst.Len() |
| if r == 0 { |
| panic(zeroDim) |
| } |
| for { |
| for i := 0; i < r; i++ { |
| dst.SetVec(i, u.norm.Rand()) |
| } |
| l := mat.Norm(dst, 2) |
| // Use l only if it is not too short. Otherwise try again. |
| const minLength = 1e-5 |
| if l > minLength { |
| dst.ScaleVec(1/l, dst) |
| return |
| } |
| } |
| } |