Public Overloads Shared Function TrendLinePolynomial( _
   ByVal s As Series, _
   ByVal degree As Integer, _
   ByVal step As Double, _
   ByVal forward As Integer, _
   ByVal backward As Integer _
) As Series

Visual Basic (Usage)	Copy Code
Dim s As Series Dim degree As Integer Dim step As Double Dim forward As Integer Dim backward As Integer Dim value As Series   value = ForecastEngine.TrendLinePolynomial(s, degree, step, forward, backward)

public static Series TrendLinePolynomial( 
   Series s,
   int degree,
   double step,
   int forward,
   int backward
)

Parameters

s

A statistical series.

degree

The degree of the polynomial which is fitted to the data set given (i.e. if degree is 2, then a quadratic is fitted).

step

The distance in the x-coordinate between two adjacent extended points. Please note that this also corresponds to the distance in the x-coordinate between the highest and lowest original data point and the first (above or below) additional evaluation point.

forward

The number of additional evaluation points which are evaluated above the x-coordinates of the original given data set.

backward

The number of additional evaluation points which are evaluated below the x-coordinates of the original given data set.

Return Value

Remark: This methods corresponds in functionality to the method of the same name within Microsoft Excel.

Remark: The difference between this method and TrendLinePolynomial, is that it allows the values of the fitted function to be evaluated over an extended range. That is, a range in the x-coordinate greater than the original given data set.

Where the extended values are evaluated?

The parameters step, forward, backward allows the position and number of additional points above and/or below the range of the values in the x-coordinate of the original data set to be given. The forward parameter specifies the number of the additional evaluation points of the fitted function which are greater than the values of the x-coordinates of the original data set. Similarly, the backward parameter specifies the number of the additional evaluation points of the fitted function which are lower than the values of the x-coordinates of the original data set. The step specifies the distance in the x-coordinate between each of the additional data points, where the first additional data point either above or below is exactly a distance of step from the points of the original data set which the highest and lowest values in the x-coordinate.

For example, consider the data set x = 1, 2, 3; y = 1, 2, 3. Now if step = 1, forward = 2, and backward = 3, then this method when applied will return a two dimensional array. This two dimensional array will have the following structure: { { -2, f(-2) } { -1, f(-1) } { 0, f(0) }{ 1, 1 } { 2, 2 }{ 3, 3 } { 4, f(4) } { 5, f(5) } }, where f(-2), f(-1), f(0), f(4), f(5) correspond to the value of the fitted functions at the points x = -2, -1, 0, 4, 5, respectively.

Reference