Quasi-Random Sequences QuickStart Sample (Visual Basic)

Imports System.Collections.Generic

Imports Extreme.Mathematics
Imports Extreme.Mathematics.Random

Namespace Extreme.Numerics.QuickStart.VB
    ' Illustrates the use of quasi-random sequences by computing
    ' a multi-dimensional integral.
    Module QuasiRandomSequences

        Sub Main()
            ' This QuickStart Sample demonstrates the use of
            ' quasi-random sequences by computing
            ' a multi-dimensional integral.

            ' We will use one million points.
            Dim length As Integer = 1000000
            ' The number of dimensions:
            Dim dimension As Integer = 5

            ' We will evaluate the function
            '
            '    Product(i = 1 -> # dimensions) |4 x(i) - 2|
            '
            ' over the hypercube 0 <= x(i) <= 1. The value of this integral
            ' is exactly 1.


            ' Create the sequence
            Dim sequence = QuasiRandom.HaltonSequence(dimension, length)

            ' Compute the integral by summing over all points
            Console.WriteLine("# iter.  Estimate")
            Dim sum As Double = 0.0
            Dim i As Integer = 0
            For Each point As Vector(Of Double) In sequence
                If i Mod 100000 = 0 Then
                    Console.WriteLine("{0,6}  {1,8:F4}", i, sum / i)
                End If

                ' Evaluate the integrand
                Dim functionValue As Double = 1.0
                For j As Integer = 0 To dimension - 1
                    functionValue *= Math.Abs(4.0 * point(j) - 2.0)
                Next
                sum += functionValue
                i = i + 1
            Next
            Console.WriteLine("Final estimate: {0,8:F4}", sum / length)
            Console.WriteLine("Exact value: 1.0000")

            ' Sobol sequences require more data And more initialization.
            ' Fortunately, different sequences of the same dimension
            ' can share much of the work And storage. The 
            ' SobolSequenceGenerator class should be used in this case

            Dim skip As Integer = 1000
            Dim sobol As SobolSequenceGenerator = New SobolSequenceGenerator(dimension, length + skip)
            ' Sobol sequences are more flexible: they let you skip
            ' a number of points at the start of the sequence.
            ' The cost of skipping points Is O(1).
            i = 0
            sum = 0.0
            For Each point As Vector(Of Double) In sobol.Generate(length, skip)
                If i Mod 100000 = 0 Then
                    Console.WriteLine("{0,6}  {1,8:F4}", i, sum / i)
                End If

                ' Evaluate the integrand
                Dim functionValue As Double = 1.0
                For j As Integer = 0 To dimension - 1
                    functionValue *= Math.Abs(4.0 * point(j) - 2.0)
                Next
                sum = sum + functionValue
                i = i + 1
            Next
            ' Print the final result.
            Console.WriteLine("Final estimate: {0,8:F4}", sum / length)
                    Console.WriteLine("Exact value: 1.0000")

                    Console.Write("Press any key to exit.")
                    Console.ReadLine()

        End Sub

    End Module

End Namespace