28 lognormalfix (#29)

* Fix calculation of sigma

Author: abeham

src/SimSharp/Core/Environment.cs

@@ -9,7 +9,6 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
-using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -530,8 +529,7 @@ public double RandLogNormal(double mu, double sigma) {
     /// <returns>A log-normal distributed random value.</returns>
     public double RandLogNormal2(IRandom random, double mean, double stdev) {
       if (stdev == 0) return mean;
-      var alpha = Math.Sqrt(mean * stdev) / mean;
-      var sigma = Math.Sqrt(Math.Log(1 + (alpha * alpha)));
+      var sigma = Math.Sqrt(Math.Log(stdev * stdev / (mean * mean) + 1));
       var mu = Math.Log(mean) - 0.5 * sigma * sigma;
       return Math.Exp(RandNormal(random, mu, sigma));
     }

src/Tests/EnvironmentTests.cs

@@ -179,7 +179,7 @@ public void PseudoRealtimeEnvTestStopTest() {
       var t = Task.Run(() => env.Run(TimeSpan.FromMinutes(1)));
       Task.Delay(TimeSpan.FromMilliseconds(200)).Wait();
       env.StopAsync();
-      Task.Delay(TimeSpan.FromMilliseconds(200)).Wait();
+      Task.Delay(TimeSpan.FromMilliseconds(500)).Wait();
       Assert.True(t.IsCompleted);
     }