/// <summary>
/// Initializes a new instance of the <see cref="ConditionalCombination"/> class.
/// </summary>
/// <param name="condition">The conditional event.</param>
/// <param name="trueCase">The scenario to be used if <paramref name="condition"/> is <c>true</c>.</param>
/// <param name="falseCase">The scenario to be used if <paramref name="condition"/> is <c>false</c>.</param>
public ConditionalCombination(
IDiscreteBooleanRandomVariable condition,
IDiscreteIntegerRandomVariable trueCase,
IDiscreteIntegerRandomVariable falseCase)
{
Debug.Assert(condition != null, "The conditional random variable cannot be null.");
Debug.Assert(trueCase != null, "The random variable for when the conditional random variable is true cannot be null.");
Debug.Assert(falseCase != null, "The random variable for when the conditional random variable is false cannot be null.");
ProbabilityDistribution = GetProbabilityDistribution(condition, trueCase, falseCase);
}
private static DiscreteValueProbabilityDistribution GetProbabilityDistribution(
IDiscreteBooleanRandomVariable condition,
IDiscreteIntegerRandomVariable trueCase,
IDiscreteIntegerRandomVariable falseCase)
{
IDictionary <int, double> valueAndProbabilities = trueCase.ProbabilityDistribution.Specification
.ToDictionary(pair => pair.Value, pair => pair.Probability * condition.ProbabilityDistribution.SuccessProbability);
foreach (ValueProbabilityPair pair in falseCase.ProbabilityDistribution.Specification)
{
double probabilityComponent = condition.ProbabilityDistribution.FailureProbability * pair.Probability;
if (valueAndProbabilities.ContainsKey(pair.Value))
{
valueAndProbabilities[pair.Value] += probabilityComponent;
}
else
{
valueAndProbabilities[pair.Value] = probabilityComponent;
}
}
return(new DiscreteValueProbabilityDistribution(valueAndProbabilities.Select(vp => new ValueProbabilityPair(vp.Key, vp.Value))));
}
