Random Number Between 2 Double Numbers

Question

Is it possible to generate a random number between 2 doubles   Example   public double GetRandomeNumber double minimum  double maximum        return Random NextDouble minimum  maximum       Then I call it with the following   double result   GetRandomNumber 1 23  5 34     Any thoughts would be appreciated

User · Answer

Use a static Random or the numbers tend to repeat in tight/fast loops due to the system clock seeding them.

public static class RandomNumbers
{
    private static Random random = new Random();
    //=-------------------------------------------------------------------
    // double between min and the max number
    public static double RandomDouble(int min, int max) 
    {
        return (random.NextDouble() * (max - min)) + min;
    }
    //=----------------------------------
    // double between 0 and the max number
    public static double RandomDouble(int max) 
    {
        return (random.NextDouble() * max);
    }
    //=-------------------------------------------------------------------
    // int between the min and the max number
    public static int RandomInt(int min, int max) 
    {   
        return random.Next(min, max + 1);
    }
    //=----------------------------------
    // int between 0 and the max number
    public static int RandomInt(int max) 
    {
        return random.Next(max + 1);
    }
    //=-------------------------------------------------------------------
 }

See also : https://docs.microsoft.com/en-us/dotnet/api/system.random?view=netframework-4.8

User · Answer

Random random   new Random     double NextDouble double minimum  double maximum           return random NextDouble   random Next minimum maximum

User · Answer

Johnny5 suggested creating an extension method  Here s a more complete code example showing how you could do this   public static class RandomExtensions       public static double NextDouble          this Random random          double minValue          double maxValue                return random NextDouble      maxValue - minValue    minValue            Now you can call it as if it were a method on the Random class   Random random   new Random    double value   random NextDouble 1 23  5 34     Note that you should not create lots of new Random objects in a loop because this will make it likely that you get the same value many times in a row  If you need lots of random numbers then create one instance of Random and re-use it

User · Answer

You could use code like this   public double getRandomNumber double minimum  double maximum        return minimum   randomizer nextDouble      maximum - minimum

User · Answer

Watch out  if you re generating the random inside a loop like for example for int i   0  i  lt  10  i     do not put the new Random   declaration inside the loop   From MSDN      The random number generation starts from a seed value  If the same   seed is used repeatedly  the same series of numbers is generated  One   way to produce different sequences is to make the seed value   time-dependent  thereby producing a different series with each new   instance of Random  By default  the parameterless constructor of the   Random class uses the system clock to generate its seed value      So based on this fact  do something as   var random   new Random     for int d   0  d  lt  7  d             Actual BOE     boes Add new LogBOEViewModel                 LogDate   criteriaDate          BOEActual   GetRandomDouble random  100  1000           BOEForecast   GetRandomDouble random  100  1000             double GetRandomDouble Random random  double min  double max         return min    random NextDouble      max - min        Doing this way you have the guarantee you ll get different double values

User · Answer

I m a bit late to the party but I needed to implement a general solution and it turned out that none of the solutions can satisfy my needs   The accepted solution is good for small ranges  however  maximum - minimum can be infinity for big ranges  So a corrected version can be this version   public static double NextDoubleLinear this Random random  double minValue  double maxValue           TODO  some validation here        double sample   random NextDouble        return  maxValue   sample     minValue    1d - sample        This generates random numbers nicely even between double MinValue and double MaxValue  But this introduces another  problem   which is nicely presented in this post  if we use such big ranges the values might seem too  unnatural   For example  after generating 10 000 random doubles between 0 and double MaxValue all of the values were between 2 9579E 304 and 1 7976E 308   So I created also another version  which generates numbers on a logarithmic scale   public static double NextDoubleLogarithmic this Random random  double minValue  double maxValue           TODO  some validation here        bool posAndNeg   minValue  lt  0d  amp  amp  maxValue  gt  0d      double minAbs   Math Min Math Abs minValue   Math Abs maxValue        double maxAbs   Math Max Math Abs minValue   Math Abs maxValue         int sign      if   posAndNeg          sign   minValue  lt  0d   -1   1      else                  if both negative and positive results are expected we select the sign based on the size of the ranges         double sample   random NextDouble            var rate   minAbs   maxAbs          var absMinValue   Math Abs minValue           bool isNeg   absMinValue  lt   maxValue   rate   2d  gt  sample   rate   2d  lt  sample          sign   isNeg   -1   1              now adjusting the limits for 0   selected range          minAbs   0d          maxAbs   isNeg   absMinValue   Math Abs maxValue                 Possible double exponents are -1022  1023 but we don t generate too small exponents for big ranges because        that would cause too many almost zero results  which are much smaller than the original NextDouble values      double minExponent   minAbs    0d   -16d   Math Log minAbs  2d       double maxExponent   Math Log maxAbs  2d       if  minExponent    maxExponent          return minValue          We decrease exponents only if the given range is already small  Even lower than -1022 is no problem  the result may be 0     if  maxExponent  lt  minExponent          minExponent   maxExponent - 4       double result   sign   Math Pow 2d  NextDoubleLinear random  minExponent  maxExponent            protecting ourselves against inaccurate calculations  however  in practice result is always in range      return result  lt  minValue   minValue    result  gt  maxValue   maxValue   result       Some tests   Here are the sorted results of generating 10 000 random double numbers between 0 and Double MaxValue with both strategies  The results are displayed with using logarithmic scale     Though the linear random values seem to be wrong at first glance the statistics show that none of them are  better  than the other  even the linear strategy has an even distribution and the average difference between the values are pretty much the same with both strategies   Playing with different ranges showed me that the linear strategy gets to be  sane  with range between 0 and ushort MaxValue with a  reasonable  minimum value of 10 78294704  for ulong range the minimum value was 3 03518E 15  int  353341   These are the same results of both strategies displayed with different scales       Edit   Recently I made my libraries open source  feel free to see the RandomExtensions NextDouble method with the complete validation

User · Answer

The simplest approach would simply generate a random number between 0 and the difference of the two numbers   Then add the smaller of the two numbers to the result

User · Answer

You could do this   public class RandomNumbers   Random       public RandomNumbers int seed    base seed           public double NextDouble double minimum  double maximum                return base NextDouble      maximum - minimum    minimum

User · Answer

If you need a random number in the range  double MinValue  double MaxValue      Because of  double MaxValue - double MinValue    double PositiveInfinity     This will be equals to NaN or PositiveInfinity random NextDouble      double MaxValue - double MinValue    Use instead   public static class RandomExtensions       public static double NextDoubleInMinMaxRange this Random random                var bytes   new byte sizeof double            var value   default double           while  true                        random NextBytes bytes               value   BitConverter ToDouble bytes  0               if   double IsNaN value   amp  amp   double IsInfinity value                   return value

User · Answer

About generating the same random number if you call it in a loop a nifty solution is to declare the new Random   object outside of the loop as a global variable   Notice that you have to declare your instance of the Random class outside of the GetRandomInt function if you are going to be running this in a loop      Why is this     you ask   Well  the Random class actually generates pseudo random numbers  with the    seed    for the randomizer being the system time  If your loop is sufficiently fast  the system clock time will not appear different to the randomizer and each new instance of the Random class would start off with the same seed and give you the same pseudo random number   Source is here   http   www whypad com posts csharp-get-a-random-number-between-x-and-y 412

User · Answer

Yes   Random NextDouble returns a double between 0 and 1   You then multiply that by the range you need to go into  difference between maximum and minimum  and then add that to the base  minimum    public double GetRandomNumber double minimum  double maximum         Random random   new Random        return random NextDouble      maximum - minimum    minimum      Real code should have random be a static member   This will save the cost of creating the random number generator  and will enable you to call GetRandomNumber very frequently   Since we are initializing a new RNG with every call  if you call quick enough that the system time doesn t change between calls the RNG will get seeded with the exact same timestamp  and generate the same stream of random numbers

User · Answer

What if one of the values is negative    Wouldn t a better idea be   double NextDouble double min  double max           if  min  gt   max              throw new ArgumentOutOfRangeException               return random NextDouble      Math Abs max-min     min

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