39 lines
1.4 KiB
Go
39 lines
1.4 KiB
Go
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// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: MIT
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package core
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import "testing"
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// TestInterpolateQueryOnKnotTakesTheLeftSegment pins the segment choice
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// for a query landing exactly on a knot: the bisection takes the first
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// knot at or above the query, so the left segment is used and the query
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// sits at its upper end with t exactly 1. With a lower y of zero the
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// interpolation is exactly the knot's own y. A repeated knot makes the
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// choice observable: the query returns the first of the repeated ys,
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// where the right segment would return the second.
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func TestInterpolateQueryOnKnotTakesTheLeftSegment(t *testing.T) {
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xs := mustFloats(t, []float64{0, 1, 2, 3})
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ys := mustFloats(t, []float64{0, 10, 20, 30})
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q := mustFloats(t, []float64{1, 2})
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out, err := Interpolate(xs, ys, q)
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if err != nil {
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t.Fatalf("Interpolate: %v", err)
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}
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for i, w := range []float64{10, 20} {
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if got := out.FloatAt(i); got != w {
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t.Fatalf("query on knot %v answered %v, want exactly %v", q.FloatAt(i), got, w)
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}
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}
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dup, err := Interpolate(
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mustFloats(t, []float64{0, 1, 1, 2}),
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mustFloats(t, []float64{10, 20, 30, 40}),
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mustFloats(t, []float64{1}))
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if err != nil {
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t.Fatalf("Interpolate: %v", err)
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}
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if got := dup.FloatAt(0); got != 20 {
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t.Fatalf("query on a repeated knot answered %v, want the left segment's 20", got)
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}
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}
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