code: public static double computeAlpha(double targetWeight, long targetAgeInSeconds)
      {
          checkArgument(targetAgeInSeconds > 0, "targetAgeInSeconds must be > 0");
          checkArgument(targetWeight > 0 && targetWeight < 1, "targetWeight must be in range (0, 1)");
  
          return -Math.log(targetWeight) / targetAgeInSeconds;
      }
docs: Compute the alpha decay factor such that the weight of an entry with age 'targetAgeInSeconds' is targetWeight'