dotproduct-bench.md

// Learn more about F# at http://docs.microsoft.com/dotnet/fsharp

open BenchmarkDotNet.Attributes
open BenchmarkDotNet.Running

module DotProduct =
    let rec dotProduct (vector1 : float []) (vector2 : float []) : float =

        if vector1 |> Array.length = 0 then
            0.0
        else
            vector1.[0] * vector2.[0] + (dotProduct (vector1 |> Array.tail) (vector2 |> Array.tail))

    let dotProductLoop (vector1 : float []) (vector2 : float []) : float =
        let mutable acc = 0.0

        for idx = 0 to vector1.Length - 1 do
            acc <- acc + (vector1.[idx] * vector2.[idx])
        
        acc

    // Fast
    let dotProductFold (vector1 : float []) (vector2 : float [])  =
        Array.fold2 (fun state x y -> state + x * y) 0.0 vector1 vector2

[<MemoryDiagnoser>]
type DotProductBench() =
    let arr1 = [| 1.0..1_000.0 |]
    let arr2 = [| 1.0..1_000.0 |]

    [<Benchmark(Baseline=true)>]
    member _.DotProduct() = DotProduct.dotProduct arr1 arr2

    [<Benchmark>]
    member _.DotProductLoop() = DotProduct.dotProductLoop arr1 arr2

    [<Benchmark>]
    member _.DotProductFold() = DotProduct.dotProductFold arr1 arr2

[<EntryPoint>]
let main argv =
    BenchmarkRunner.Run<DotProductBench>() |> ignore
    0 // return an integer exit code

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.19042.1288 (20H2/October2020Update)
AMD Ryzen 9 5900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK=6.0.100-rc.2.21505.57
  [Host]     : .NET 6.0.0 (6.0.21.48005), X64 RyuJIT DEBUG
  DefaultJob : .NET 6.0.0 (6.0.21.48005), X64 RyuJIT

Method	Mean	Error	StdDev	Ratio	Gen 0	Gen 1	Allocated
DotProduct	320,534.9 ns	1,738.55 ns	1,626.24 ns	1.000	480.4688	18.0664	8,040,000 B
DotProductLoop	625.4 ns	1.93 ns	1.71 ns	0.002	-	-	-
DotProductFold	1,105.1 ns	10.77 ns	10.07 ns	0.003	-	-	-