matrix:forecast-linear-growth

matrix:forecast-linear-growth data-list

Reports a four-element list of the form:

[ forecast constant slope R² ]

The forecast is the predicted next value that would follow in the sequence given by the data-list input, based on a linear trend-line. Normally data-list will contain observations on some variable, Y, from time t = 0 to time t = (n-1) where n is the number of observations. The forecast is the predicted value of Y at t = n. The constant and slope are the parameters of the trend-line

Y = *constant* + *slope* * t.

The R² value measures the goodness of fit of the trend-line to the data, with an R² = 1 being a perfect fit and an R² of 0 indicating no discernible trend. Linear growth assumes that the variable Y grows by a constant absolute amount each period.

;; a linear extrapolation of the next item in the list.
print matrix:forecast-linear-growth [20 25 28 32 35 39]
=> [42.733333333333334 20.619047619047638 3.6857142857142824 0.9953743395474031]
;; These results tell us:
;; * the next predicted value is roughly 42.7333
;; * the linear trend line is given by Y = 20.6190 + 3.6857 * t
;; * Y grows by approximately 3.6857 units each period
;; * the R^2 value is roughly 0.9954 (a good fit)