- not so Frequently Asked Questions -
not so FAQ
There are two kinds of tics --- the major tics and the minor tics.
Numbers (figures) on axes are drawn at the major tics only. At the default
the minor tics are not shown except for a logarithmic scale.
set {x|y}tics
command changes the major tics.
gnuplot& set xtics 2
gnuplot& set ytics 0,200
gnuplot& plot x**3
Only an increment is defined for the X-axis, so that the positions
of tics become -10, -8, ... +10. For the Y-axis, the starting value
and the increment are both given. Gnuplot makes tics at 0, 200, 400...
In this case there is no tic mark where Y is negative. You can also
give the last value like, set ytics 0,200,600.
The minor tics can be controlled by
set m{x|y}tics .
Intervals between each major tic are divided by this value. The
following example is to draw a mid-point between each major tics in
the above figure.
gnuplot& set mxtics 2
gnuplot& set mytics 2
It is possible to place an arbitrary text at the tics position
instead of the numbers. you can write "April", "May", "June", and
"July" at the positions X=1,2,3, and 4, by the following way.
gnuplot& set xtics ("April" 1, "May" 2, "June" 3, "July" 4)
gnuplot& plot "test.dat" using 1:2:3 notitle with boxes,\
"test.dat" using 1:2
notitle with lines
As can be seen, the minor tics are ignored when
the major tics are defined in this syntax.
Command set ticscale
n m changes the length
(size) of tics.
The major tics are multiplied by the provided value
n, while the minor tics are multiplied by m. If m
is omitted, the minor tics are half length of the major tics.
set ticscale 1 1 makes the same length of the major and
minor tics.
The tics are drawn inwards. To make it outwards,
set tics out .
The default
"%g". In the log scaling, the labels are written by the "F" format
like 0.01, 1000, etc. if the range is more than 0.0001 and less than
100000. If the numbers are outside this range, the format is changed
into "E" which gives the numbers such as 1e-05, 1e+06, etc.
To express numbers by power to base 10, change the label format
into "10^{%L}" by the command set format. "%L" gives the
value of power to base 10. The X window terminal cannot show
super-scripts, so use the postscript terminal.
gnuplot& set format y "10^{%L}"
gnuplot& set terminal postscript eps enhanced
gnuplot& set ylabel "Y-AXIS" 2,0
When the format is defined like this, the distance between
the Y-axis and its label becomes wider. This can be adjusted by
the offset option of the set ylabel command. In this
case the Y-axis label was moved to right by 2 character-widths.
The format of the tic-labels can be changed by set format
command. The syntax is set format + axis name (X, Y, Z, XY,
format string. This string is similar to the format string
in C-language. The next example tells gnuplot to show the tic-labels
by ten letters with three digits following the decimal point.
gnuplot& set format x "%10.3f"
The syntax for the digit is "%" + (total length).(precision).
floating number 6.2 represents
that the total length is six and there are two digits following the
decimal point, so that tic-labels are shown as "5.00". It is possible
to omit the length or precision, like 6 or .2.
The default values are used for the omitted number.
The display format is expressed by one letter -- 'f', 'e', 'E',
'g', 'x', 'X', 'o', 't', 'l', 's', 'T', 'L', 'S', 'c', and 'P'. The
default is "%g".
When the tics-labels can be expressed by appropriate
length and precision, those are written by "%.0f" format, otherwise
"%e" format is used. The next table shows the difference among the
format 'f', 'e', 'x', and 'o'. The formats 'e' and 'E' are the same
except that the written text is 'e' or 'E'. The format "%O" exists in
the gnuplot manual, but it does not work (bug ?)
Format Explanation
Example (underscore means
exponential
_5.0000e+01
hexadecimal
The formats, 't', 'l', 'T', and 'L' are related to log-scale plot.
Let's draw a function y=exp(-x)+exp(x) in the X range of
[-10:10]. Firstly this function is shown in a non-log scale.
to compare those formats, the tics are shown in three formats at the
same time.
gnuplot& set format y "%T %t %g"
gnuplot& plot exp(-x)+exp(x)
You can specify the different kinds of format simultaneously just
like this case --- three numbers are written on the Y-axis.
one is for "%T", the next is "%t", and the third is "%g",
respectively. As you can see, "%t" represents the mantissa to base 10,
and "%T" represents the power to base 10. Therefore the number
expressed by the "%g" format is A x 10^B, where A is given by "%t" and
B is "%T".
Now, the figure in log-scale becomes:
gnuplot& set logscale y
gnuplot& replot
The numbers expressed by the format "%t" become unity, and "%T"
gives log of the Y-axis. So
set format "%T"
displays power
to base 10 along the Y-axis. If the terminal can display a
super-script - like Postscript terminal, the format "10^{%T}" gives an
exponential expression.
Usually 't' and 'l', 'T' and 'L' give the same results in a usual
log-scaling. If one uses the different base for log-scaling, those
give different results. The format 't' and 'T' give mantissa and power
to base 10, while 'l' and 'L' give those to an arbitrary base which is
defined by set logscale axis base command. But base 10
is commonly used for log-scaling, so you can regard those the
You can include various letters and texts as well as the numbers
in format. For example,
set format x "%g km"
values in 'g' format and unit "km".
This is an application of
gnuplot& set format x ""
from Chriss in Univ. Tuebingen. Thanks !
Generally log-tics appear at the power of 10,
(1,10,100...). Sometimes it is helpful to understand graphs if you
make tics between them, especially in case the range of axis is not so
large (for example, ratio of the max to min is 10 or 100). Gnuplot
writes values at the major tics specified by
set {x|y}tic
only, so you need to define the positions where you want to write
gnuplot& set logscale y
gnuplot& set yrange [1:50]
gnuplot& set ytics (1,2,5,10,20,50)
gnuplot& set format y "%2.0t{/Symbol \327}10^{%L}"
gnuplot& set lmargin 8
gnuplot& set terminal postscript eps enhanced
gnuplot& plot exp(x)/x
The Postscript symbol in the set format line becomes
"center dot". To change it into "cross", use {/Symbol \264}.
The method explained here does not work on some systems. For
example, when the number 50.0 is formatted with "%t" and "%L", some
system gives the values 5.0 and 1 (namely 50.0 = 5.0E+01), so it works
But other systems give the value of 0.5 and 2 (50.0 =
0.5E+02). In this case the value on the graph axis becomes 0x10^2.
(zero in log-graph ????)