gnuplot documentation

60 PLOT gnuplot 4.3 71
# Gnu population in Antarctica since 1965
1965 103
1970 55
1975 34
1980 24
1985 10
60.2.5 Index
The index keyword allows only some of the data sets in a multi-data-set file to be plotted.
Syntax:
plot ’file’ index { {{:}:} | "" }
Data sets are separated by pairs of blank records. index selects only set ; index :
selects sets in the range to ; and index :: selects indices , +,
+2, etc., but stopping at . Following C indexing, the index 0 is assigned to the first data
set in the file. Specifying too large an index results in an error message. If index is not specified, all
sets are plotted as a single data set.
Example:
plot ’file’ index 4:5
index ’’ selects the data set with name ’’. Names are assigned to data sets in comment
lines. The comment character and leading white space are removed from the comment line. If the
resulting line starts with , the following data set is now named and can be selected.
Example:
plot ’file’ index ’Population’
Please note that every comment that starts with will name the following data set. To avoid
problems use a naming scheme like e.g. ’== Popolation ==’ or ’[Population]’.
60.2.6 Smooth
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 | frequency | csplines | acsplines | bezier | sbezier}
unique and frequency plot 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 (p. 129)) 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 autoscale is not in effect, and the smooth option is either acspline or cspline, the sampling of the
generated curve is done across the intersection of the x range covered by the input data and the fixed
abscissa range as defined by set xrange.
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 and frequency, four for acsplines, and three for the others.
The smooth options have no effect on function plots.