/// <summary>
/// Develops the model's cumulative triangle into a run-off square with the calculated factors of the additive method.
/// </summary>
/// <returns>The projected run-off square according to the additive method.</returns>
protected override IReadOnlySquare CalculateProjection()
{
ISquare calc = new Square(Triangle.Periods);
calc.SetColumn(Triangle.GetColumn(0), 0);
for (int i = 0; i < calc.Periods - 1; i++)
{
IEnumerable <decimal> calculatedValues = _premiums
.Skip(calc.Periods - i - 1)
.Select(x => Factors[i + 1] * x)
.Zip(calc.GetColumn(i).Skip(calc.Periods - i - 1), (x, y) => x + y);
calc.SetColumn(_cumulativeTriangle.GetColumn(i + 1).Concat(calculatedValues), i + 1);
}
return(calc.AsReadOnly());
}