The Interpolate() function finds the y value corresponding to a given x value between two points (x1, y1 and x2, y2). A linear interpolation is applied to the values. You might use Interpolate() to calculate missing values between data points.
Interpolate( x, x1, y1, x2, y2, ... );
Interpolate( x, xmatrix, ymatrix );
Interpolate( 23, [20 21 22 24 25], [59 62 56 69 75] );
62.5
The value 62.5 is halfway between the y values 56 and 69, just as 23 is halfway between the x values 22 and 24.
The data points in each list or matrix must create a positive slope. For example, Interpolate(2,1,1,3,3) returns 2. However, Interpolate(2,3,3,1,1) returns a missing value (.).
Interpolate is best used for continuous data, but Step() is for discrete data. See Step for details.