public void TestNormalDistGetZScore()
{
var testSubject = new NormalDistEquation {
Mean = 0, StdDev = 1
};
var testResult = testSubject.GetZScoreFor(0);
Assert.IsTrue(testResult >= 0.499);
testResult = testSubject.GetZScoreFor(1);
Assert.IsTrue(testResult >= 0.34134);
}
/// <summary>
/// Gets a date around a semester's end moving
/// out (x) number of years, at random, from <see cref="fromHere"/>
/// </summary>
/// <param name="fromHere"></param>
/// <param name="eq">Normal dist which determines (x) mentioned above.</param>
/// <param name="monthOfMayOnly">Force the random date to occur only in the month of May</param>
/// <returns></returns>
public static DateTime GetRandomGraduationDate(DateTime fromHere, NormalDistEquation eq, bool monthOfMayOnly = false)
{
var years = Etx.RandomValueInNormalDist(eq);
var gradDt = fromHere.AddYears((int)Math.Round(years));
var validMonths = monthOfMayOnly ? new[] { 5 } : new[] { 5, 12 };
while (!validMonths.Contains(gradDt.Month))
{
gradDt = gradDt.AddMonths(1);
}
gradDt = new DateTime(gradDt.Year, gradDt.Month, Etx.RandomInteger(12, 28));
return(gradDt);
}
public void TestGetRandomGraduationDate()
{
var normDist = new NormalDistEquation {
Mean = 4.469, StdDev = 0.5145
};
var atDate = DateTime.Today;
var minYears = (int)Math.Floor(4.469 - 0.5145 * 3);
var testResult = AmericanEducation.GetRandomGraduationDate(atDate, normDist);
System.Diagnostics.Debug.WriteLine(testResult);
Assert.IsTrue(DateTime.Today.AddYears(minYears * -1) < testResult);
Assert.IsTrue(new[] { 5, 12 }.Contains(testResult.Month));
}
public static IEnumerable <double> RandomValuesFromAverage(double mean = 0.0D, int count = 128)
{
//get some random number of items
var matchSign = mean < 0 ? -1D : 1;
count = count <= 1 ? RandomInteger(2, 128) : count;
mean = Math.Abs(mean);
var stdDev = mean * 0.125D;
var normalDist = new NormalDistEquation {
Mean = mean, StdDev = stdDev
};
var randList = new List <double>();
for (var i = 0; i < count; i++)
{
randList.Add(RandomValueInNormalDist(normalDist) * matchSign);
}
return(randList);
}
public void TestNormalDist()
{
var testSubject = new NormalDistEquation()
{
Mean = 0, StdDev = 1
};
Console.WriteLine(string.Format("{0}\t{1}", "x", "f(x)"));
for (var i = 0; i <= 30; i++)
{
for (var j = 0; j < 10; j++)
{
var z = i * 0.1 + j * 0.01;
var testResult = testSubject.SolveForY(z);
//var testResult = (z - testSubject.Mean)/testSubject.StdDev;
//System.Diagnostics.Debug.Write(string.Format(" {0} ", z));
Console.WriteLine(string.Format("{0}\t{1}", z, testResult));
}
}
}
public static double RandomValueInNormalDist(NormalDistEquation eq, int sigma = 3)
{
if (eq == null)
{
throw new ArgumentNullException(nameof(eq));
}
var minRand = eq.Mean - (eq.StdDev * sigma);
var maxRand = eq.Mean + (eq.StdDev * sigma);
if (minRand < Int32.MinValue || maxRand > Int32.MaxValue)
{
throw new ArgumentException("The random number generator is limited to int max 2^31 value.");
}
for (var i = 0; i < 1024; i++)
{
//guess some value w/i 3 std dev's
var someValue = RandomDouble(minRand, maxRand);
//get the probability of that guess
var zscore = eq.GetZScoreFor(someValue);
//zscore
var attempt = RandomDouble(0, 5) * 0.1;
//try getting a value with that probability
var isGe = attempt >= zscore;
//when succeed - return some value
if (isGe)
{
return(someValue);
}
}
return(eq.Mean);
}
