gnuplot includes a few general-purpose routines for interpolation and approximation of data; these are grouped under the smooth option. More sophisticated data processing may be performed by preprocessing the data externally or by using fit with an appropriate model.
Syntax:
smooth {unique | csplines | acsplines | bezier | sbezier}
unique plots the data after making them monotonic. Each of the other routines uses the data to determine the coefficients of a continuous curve between the endpoints of the data. This curve is then plotted in the same manner as a function, that is, by finding its value at uniform intervals along the abscissa (see set samples) and connecting these points with straight line segments (if a line style is chosen).
If autoscale is in effect, the ranges will be computed such that the plotted curve lies within the borders of the graph.
If too few points are available to allow the selected option to be applied, an error message is produced. The minimum number is one for unique, four for acsplines, and three for the others.
The smooth options have no effect on function plots.
acsplines
bezier
csplines
sbezier
unique