spline(C)

spline -- interpolate a smooth curve from a set of points

Syntax

spline [ -a m ] [ -k k ] [ -n n ] [ -p ] [ -x l [ u ] ]

Description

spline reads pairs of numbers from the standard input as the abscissa and ordinate values (x and y coordinates) of a function. It produces a similar set, approximately equally spaced and including the input set, on the standard output. The cubic spline output has two continuous derivatives, and enough points to look smooth when plotted.

spline accepts the following options, each as a separate argument:

-a m: Supplies abscissa (x-axis) values automatically with a spacing of m if they are missing from the input. The default spacing is 1.
-k k: Sets the constant used in boundary value computation to k; the second derivative at each boundary is set to k times the adjacent first derivative. The default value of k is 0.0 which gives a natural cubic spline with a zero second derivative on both its boundaries.
-n n: Spaces output points so that approximately n intervals occur between the lower and upper limits defined for the abscissa (x-axis) by -x. The default number of intervals is 100.
-p: Makes the output periodic: that is, spline matches derivatives at each end. First and last input values should normally have the same value.
-x l [ u ]: Defines the lower (l) and upper (u) limits on the abscissa (x-axis). Normally these limits are calculated from the data with a default lower limit of 0.

Limitations

If the data does not increase monotonically along the x-axis, spline reproduces the input without interpolating extra points.

The input data is limited to 1000 points.