// DescribeTree calculates the persistence landscape functions λₖ for the interval
// data in the provided interval tree. fn is called for each position t of the span
// of the interval data with the values for t and the k λ functions at t.
// Explicit zero values for a λₖ(t) are included only at the end points of intervals
// in the span. Note that intervals stored in the tree must have unique id values
// within the tree.
func DescribeTree(it *interval.IntTree, fn func(t int, λₜ []int)) {
if it == nil || it.Len() == 0 {
return
}
var (
h endHeap
t = it.Root.Range.Start
end = it.Root.Range.End
last = it.Max().ID()
l []int
)
it.Do(func(iv interval.IntInterface) (done bool) {
if s := iv.Range().Start; s >= t || iv.ID() == last {
if iv.ID() == last {
heap.Push(&h, iv)
s, iv = iv.Range().End, nil
}
for ; t < s; t++ {
for len(h) > 0 && h[0].Range().End <= t {
heap.Pop(&h)
l = append(l, 0)
}
for _, iv := range h {
r := iv.Range()
if r.Start == t {
l = append(l, 0)
}
if v := max(0, min(t-r.Start, r.End-t)); v > 0 {
l = append(l, v)
}
}
sort.Ints(l)
reverse(l)
fn(t, l)
l = l[:0]
}
}
if iv != nil {
heap.Push(&h, iv)
} else {
for ; t <= end; t++ {
for len(h) > 0 && h[0].Range().End <= t {
heap.Pop(&h)
l = append(l, 0)
}
for _, iv := range h {
r := iv.Range()
if r.Start == t {
l = append(l, 0)
}
if v := max(0, min(t-r.Start, r.End-t)); v > 0 {
l = append(l, v)
}
}
sort.Ints(l)
reverse(l)
fn(t, l)
l = l[:0]
}
}
return
})
}
