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tiny linear interpolation library for go

# sgreben/piecewiselinear

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# piecewiselinear

A tiny library for linear interpolation. `O(log(N))` per evaluation for `N` control points (and `O(1)` in a special case).

`import "github.com/sgreben/piecewiselinear"`

## Get it

`go get -u "github.com/sgreben/piecewiselinear"`

## Use it

```import "github.com/sgreben/piecewiselinear"

func main() {
f := piecewiselinear.Function{Y:[]float64{0,1,0}} // range: "hat" function
f.X = []float64{0, 0.5, 1}                        // domain: equidistant points along X axis
fmt.Println(
f.At(0),      // f.At(x) evaluates f at x
f.At(0.25),
f.At(0.5),
f.At(0.75),
f.At(1.0),
f.At(123.0),  // outside its domain X the function is constant 0
f.At(-123.0), //

f.Area(),
f.AreaUpTo(0.5),
)
// Output:
// 0 0.5 1 0.5 0 0 0 0.5 0.25
}```

### Fast special case

If the control points are uniformly spaced, `piecewiselinear.FunctionUniform` is much faster (no search required):

```import "github.com/sgreben/piecewiselinear"

func main() {
f := piecewiselinear.FunctionUniform{Y: []float64{0, 1, 0}} // range: "hat" function
f.Xmin, f.Xmax = 0, 1                                       // domain: equidistant points along X axis
fmt.Println(
f.At(0), // f.At(x) evaluates f at x
f.At(0.25),
f.At(0.5),
f.At(0.75),
f.At(1.0),
f.At(123.0),  // outside its domain X the function is constant 0
f.At(-123.0), //

f.Area(),
f.AreaUpTo(0.5),
)
// Output:
// 0 0.5 1 0.5 0 0 0 0.5 0.25
}```

## Benchmarks

On an Apple M1 Pro:

• 6ns per evaluation (`.At(x)`) for 10 control points
• 320ns per evaluation for 10 million control points.

and, for `FunctionUniform`, 2ns per evaluation regardless of the number of control points.

``````goos: darwin
goarch: arm64
pkg: github.com/sgreben/piecewiselinear
BenchmarkAt4-10                 230890022                5.499 ns/op           0 B/op          0 allocs/op
BenchmarkAt8-10                 199668106                6.084 ns/op           0 B/op          0 allocs/op
BenchmarkAt10-10                192352903                6.206 ns/op           0 B/op          0 allocs/op
BenchmarkAt100-10               138742411                8.613 ns/op           0 B/op          0 allocs/op
BenchmarkAt1k-10                46360660                25.50 ns/op            0 B/op          0 allocs/op
BenchmarkAt10k-10               16649996                70.02 ns/op            0 B/op          0 allocs/op
BenchmarkAt100k-10              11696936               100.4 ns/op             0 B/op          0 allocs/op
BenchmarkAt1M-10                 8512652               140.6 ns/op             0 B/op          0 allocs/op
BenchmarkAt10M-10                3769648               320.4 ns/op             0 B/op          0 allocs/op
BenchmarkUniformAt10M-10        571224222                2.185 ns/op           0 B/op          0 allocs/op
``````

## About

tiny linear interpolation library for go

v1.2.0 Latest
Dec 9, 2023

## Packages 0

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