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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 samplemv
import (
"math"
"testing"
"golang.org/x/exp/rand"
"gonum.org/v1/gonum/mat"
"gonum.org/v1/gonum/stat/distmv"
)
func TestHalton(t *testing.T) {
for cas, test := range []struct {
n int
d int
}{
{10, 1},
{100, 2},
{1000, 3},
} {
src := rand.New(rand.NewSource(1))
// Generate the samples.
batch := mat.NewDense(test.n, test.d, nil)
Halton{Kind: Owen, Q: distmv.NewUnitUniform(test.d, nil), Src: src}.Sample(batch)
// In each dimension, the samples should be stratefied according to the
// prime for that dimension. There should be at most 1 sample per
// 1/b^k block, where k is log(n)/log(b).
for d := 0; d < test.d; d++ {
b := float64(nthPrime(d))
fk := math.Log(float64(test.n)) / math.Log(b)
k := math.Ceil(fk)
den := math.Pow(b, k)
m := make(map[int]int)
for i := 0; i < test.n; i++ {
bucket := int(batch.At(i, d) * den)
m[bucket]++
}
for bucket, n := range m {
if n > 1 {
t.Errorf("case %d: bucket %v has %v samples", cas, bucket, n)
}
}
}
}
}
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