GNUPlot Manual
GNUPlot Manual
GNUPlot Manual
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28 PLOT gnuplot 4.0 39<br />
28.1 Data-file<br />
Discrete data contained in a file can be displayed by specifying the name of the data file (enclosed in<br />
single or double quotes) on the plot command line.<br />
Syntax:<br />
plot ’’ {index }<br />
{every }<br />
{thru }<br />
{using }<br />
{smooth }<br />
The modifiers index, every, thru, using, and smooth are discussed separately. In brief, index selects<br />
which data sets in a multi-data-set file are to be plotted, every specifies which points within a single<br />
data set are to be plotted, using determines how the columns within a single record are to be interpreted<br />
(thru is a special case of using), and smooth allows for simple interpolation and approximation. (splot<br />
has a similar syntax, but does not support the smooth and thru options.)<br />
Data files should contain at least one data point per record (using can select one data point from the<br />
record). Records beginning with # (and also with ! on VMS) will be treated as comments and ignored.<br />
Each data point represents an (x,y) pair. For plots with error bars or error bars with lines (see set style<br />
errorbars (p. 98) or set style errorlines (p. 99)), each data point is (x,y,ydelta), (x,y,ylow,yhigh),<br />
(x,y,xdelta), (x,y,xlow,xhigh), or (x,y,xlow,xhigh,ylow,yhigh).<br />
In all cases, the numbers of each record of a data file must be separated by white space (one or more<br />
blanks or tabs) unless a format specifier is provided by the using option. This white space divides<br />
each record into columns. However, whitespace inside a pair of double quotes is ignored when counting<br />
columns, so the following datafile line has three columns:<br />
1.0 "second column" 3.0<br />
Data may be written in exponential format with the exponent preceded by the letter e, E, d, D, q, or Q.<br />
Only one column (the y value) need be provided.<br />
starting at 0.<br />
If x is omitted, gnuplot provides integer values<br />
In datafiles, blank records (records with no characters other than blanks and a newline and/or carriage<br />
return) are significant — pairs of blank records separate indexes (see plot datafile index (p. 40)).<br />
Data separated by double blank records are treated as if they were in separate data files.<br />
Single blank records designate discontinuities in a plot; no line will join points separated by a blank<br />
records (if they are plotted with a line style).<br />
If autoscaling has been enabled (set autoscale), the axes are automatically extended to include all<br />
datapoints, with a whole number of tic marks if tics are being drawn. This has two consequences: i) For<br />
splot, the corner of the surface may not coincide with the corner of the base. In this case, no vertical<br />
line is drawn. ii) When plotting data with the same x range on a dual-axis graph, the x coordinates may<br />
not coincide if the x2tics are not being drawn. This is because the x axis has been autoextended to a<br />
whole number of tics, but the x2 axis has not. The following example illustrates the problem:<br />
reset; plot ’-’, ’-’ axes x2y1<br />
1 1<br />
19 19<br />
e<br />
1 1<br />
19 19<br />
e<br />
To avoid this, you can use the fixmin/fixmax feature of the set autoscale command, which turns off<br />
the automatic extension of the axis range upto the next tic mark.<br />
28.1.1 Every<br />
The every keyword allows a periodic sampling of a data set to be plotted.