public override int HandleChoice(int valueCount)
{
++_choiceIndex;
// If we have a preselected value that we should choose for the current path, return it
var chosenValuesMaxIndex = _chosenValues.Count - 1;
if (_choiceIndex <= chosenValuesMaxIndex)
{
return(_chosenValues[_choiceIndex].OptionIndex);
}
// We haven't encountered this choice before; store the value count and return the first value
_valueCount.Push(valueCount);
var newChosenValue =
new LtmcChosenValue
{
OptionIndex = 0,
Probability = GetProbabilityOfPreviousPath() / valueCount //placeholder value (for non deterministic choice)
};
_chosenValues.Push(newChosenValue);
return(0);
}
public void Push(LtmcChosenValue value)
{
if (_memoryBuffer.SizeInBytes <= Count * sizeof(LtmcChosenValue))
{
_memoryBuffer.Resize(_memoryBuffer.SizeInBytes * 2, zeroMemory: true);
_buffer = (LtmcChosenValue *)_memoryBuffer.Pointer;
}
_buffer[Count++] = value;
}
/// <summary>
/// Sets the choices that should be made during the next step.
/// </summary>
/// <param name="choices">The choices that should be made.</param>
internal override void SetChoices(int[] choices)
{
Requires.NotNull(choices, nameof(choices));
foreach (var choice in choices)
{
var newChosenValue =
new LtmcChosenValue
{
Probability = Probability.One,
OptionIndex = choice
};
_chosenValues.Push(newChosenValue);
_valueCount.Push(0);
}
}
public override bool PrepareNextPath()
{
if (_choiceIndex != _valueCount.Count - 1)
{
throw new NondeterminismException();
}
// Reset the choice counter as each path starts from the beginning
_choiceIndex = -1;
// If this is the first path of the state, we definitely have to enumerate it
if (_firstPath)
{
_firstPath = false;
return(true);
}
// Let's go through the entire stack to determine what we have to do next
while (_chosenValues.Count > 0)
{
// Remove the value we've chosen last -- we've already chosen it, so we're done with it
var chosenValue = _chosenValues.Remove();
// If we have at least one other value to choose, let's do that next
if (_valueCount.Peek() > chosenValue.OptionIndex + 1)
{
var previousProbability = GetProbabilityUntilIndex(_valueCount.Count - 2);
var valueCount = _valueCount.Peek();
var newChosenValue =
new LtmcChosenValue
{
OptionIndex = chosenValue.OptionIndex + 1,
Probability = previousProbability / valueCount //placeholder value (for non deterministic choice)
};
_chosenValues.Push(newChosenValue);
return(true);
}
// Otherwise, we've chosen all values of the last choice, so we're done with it
_valueCount.Remove();
}
// If we reach this point, we know that we've chosen all values of all choices, so there are no further paths
return(false);
}
public override void SetProbabilityOfLastChoice(Probability probability)
{
var probabilitiesOfChosenValuesMaxIndex = _chosenValues.Count - 1;
// If this part of the path has previously been visited we do not change the value
// because this value has already been set by a previous call of SetProbabilityOfLastChoice.
// Only if we explore a new part of the path the probability needs to be written.
// A new part of the path is explored, iff the previous HandleChoice pushed a new placeholder
// value onto the three stacks).
if (_choiceIndex == probabilitiesOfChosenValuesMaxIndex)
{
_chosenValues[_choiceIndex] =
new LtmcChosenValue
{
OptionIndex = _chosenValues[_choiceIndex].OptionIndex,
Probability = GetProbabilityOfPreviousPath() * probability
};
}
}
internal override void ForwardUntakenChoicesAtIndex(int choiceIndexToForward)
{
// This method is called when it is assumed, that choosing anything different at choiceIndex
// leads to the same state as the path until the last choice.
// Thus, we can simply revert this unnecessary choice and add the probability of the unmade alternatives
// of the reverted choice to the last choice.
// Note, very small numbers get multiplied and summarized. Maybe type double is too imprecise.
if (_valueCount[choiceIndexToForward] == 0)
{
return; //Nothing to do
}
Assert.That(_chosenValues[choiceIndexToForward].OptionIndex == 0, "Only first choice can be made deterministic.");
// We disable a choice by setting the number of values that we have yet to choose to 0, effectively
// turning the choice into a deterministic selection of the value at index 0
var oldProbabilityUntilDeterministicChoice = GetProbabilityUntilIndex(choiceIndexToForward - 1).Value;
var oldProbabilityOfDeterministicChoice = GetProbabilityUntilIndex(choiceIndexToForward).Value;
var differenceProbabilityToAdd = oldProbabilityUntilDeterministicChoice - oldProbabilityOfDeterministicChoice;
var probabilityOfLastChoicePath = GetProbabilityUntilIndex(LastChoiceIndex).Value;
var newValueOfLastChoice = (probabilityOfLastChoicePath + differenceProbabilityToAdd);
// set the calculated value
_chosenValues[LastChoiceIndex] =
new LtmcChosenValue
{
OptionIndex = _chosenValues[LastChoiceIndex].OptionIndex,
Probability = new Probability(newValueOfLastChoice)
};
// Set the alternatives to zero.
_valueCount[choiceIndexToForward] = 0;
}