Weibull.cs

using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Exceptions;
using Waher.Script.Model;
using Waher.Script.Objects;
using Waher.Script.Objects.VectorSpaces;
 
namespace Waher.Script.Statistics.Functions.RandomNumbers
{
    public class Weibull : FunctionMultiVariate
    {
        private static readonly ArgumentType[] argumentTypes3Parameters = new ArgumentType[] { ArgumentType.Scalar, ArgumentType.Scalar, ArgumentType.Scalar };
        private static readonly ArgumentType[] argumentTypes2Parameters = new ArgumentType[] { ArgumentType.Scalar, ArgumentType.Scalar, };
 
        public Weibull(ScriptNode Shape, ScriptNode Scale, ScriptNode N, int Start, int Length, Expression Expression)
            : base(new ScriptNode[] { Shape, Scale, N }, argumentTypes3Parameters, Start, Length, Expression)
        {
        }
 
        public Weibull(ScriptNode Shape, ScriptNode Scale, int Start, int Length, Expression Expression)
            : base(new ScriptNode[] { Shape, Scale }, argumentTypes2Parameters, Start, Length, Expression)
        {
        }
 
        public override string FunctionName => nameof(Weibull);
 
        public override string[] DefaultArgumentNames
        {
            get { return new string[] { "shape", "scale", "N" }; }
        }
 
        public override IElement Evaluate(IElement[] Arguments, Variables Variables)
        {
            switch (Arguments.Length)
            {
                case 2:
                    double Shape = Expression.ToDouble(Arguments[0].AssociatedObjectValue);
                    double Scale = Expression.ToDouble(Arguments[1].AssociatedObjectValue);
 
                    return new DoubleNumber(NextDouble(Shape, Scale));
 
                case 3:
                default:
                    Shape = Expression.ToDouble(Arguments[0].AssociatedObjectValue);
                    Scale = Expression.ToDouble(Arguments[1].AssociatedObjectValue);
                    double d = Expression.ToDouble(Arguments[2].AssociatedObjectValue);
                    int N = (int)Math.Round(d);
                    if (N < 0 || N != d)
                        throw new ScriptRuntimeException("N must be a non-negative integer.", this);
 
                    double[] v = new double[N];
                    int i;
 
                    for (i = 0; i < N; i++)
                        v[i] = NextDouble(Scale, Shape);
 
                    return new DoubleVector(v);
            }
        }
 
        public static double NextDouble(double Shape, double Scale)
        {
            if (Shape <= 0)
                throw new ArgumentOutOfRangeException("Must be positive.", nameof(Shape));
 
            if (Scale <= 0)
                throw new ArgumentOutOfRangeException("Must be positive.", nameof(Scale));
 
            return Math.Pow(-Math.Log(Uniform.NextDouble()), 1 / Shape) * Scale;
        }
 
    }
 
}