optimal_span: Calculates the optimal span for a loess spline smoother based...
In khufkens/cropmonitor: IFPRI cellphone based crop monitoring application

Calculates the optimal span for a loess spline smoother based upon the bayesian information criterion (BIC).

1 2	optimal_span(y, x = NULL, weights = NULL, start = 0.01, step = 0.01, label = NULL, plot = FALSE)

`y:`	a vector with measurement values to smooth
`x:`	a vector with dates / time steps
`weights:`	optional values to weigh the loess fit with
`step:`	span increment size

## Not run: 
# Internal function only, should not be used stand-alone.

l = sin(1,10,0.01)
l = l + runif(length(l)))
optimal.span(l, plot = TRUE)

## End(Not run)