Exponential Smoothing

expSmoothing(y :: Vector, λ :: Real; startValue::Bool = true, v_0::Real = 0.0)

Simple exponential smoothing with smoothing factor λ. If startValue equals true,
v_0 will be used as initial value, otherwise the first element of y (y[1])
will be selected as starting value.
Using y[1] as starting value will result in a different mathematical function.