not so FAQ

• Legend
• Tics
• Label
• 2-D Plot
• 3-D Plot
• Polar Coordinate
• Parametric Functions
• Data File
• After Plotting
• Miscellaneous Stuff
  • 
    ternary operator

  • 
    broken function

  • 
    loop

  • 
    least-squares fitting (I)

  • 
    least-squares fitting (II)

  • 
    dumb terminal

  • 
    many kinds of lines

  • 
    write a value

Miscellaneous Stuff (No.4)

How do I make a figure with many kinds of lines ?

The number of line-kinds gnuplot can handle depends on the
terminal. Lines in a graph you can distinguish by

Line Type (solid, dotted, dot-dashed)
Thickness (heavy, light)
Colors
Lines with Symbols

Some terminal cannot draw a dotted line, and some cannot change
the thickness. Then the number of possible combination is limited. The
following explanation is to use many kinds of lines in the postscript
terminal.

Define the linetype by set linestyle
command. If you are using gnuplot ver.4, use set style line instead.
Here we use 4 line-types, those are the solid, dashed, dotted, and
dot-dashed lines. The IDs of 1, 2, 3, and 6 are assigned for them in the
postscript terminal. With those line-types, we use thick (width 3) and thin
(width 1) lines for each of them. We get 8 line-kinds now.

gnuplot> set term postscript eps enhanced
gnuplot> set linestyle 1 lt 1 lw 1
gnuplot> set linestyle 2 lt 2 lw 1
gnuplot> set linestyle 3 lt 3 lw 1
gnuplot> set linestyle 4 lt 6 lw 1
gnuplot> set linestyle 5 lt 1 lw 3
gnuplot> set linestyle 6 lt 2 lw 3
gnuplot> set linestyle 7 lt 3 lw 3
gnuplot> set linestyle 8 lt 6 lw 3
gnuplot> set xrange [-pi:pi]
gnuplot> plot sin(  x) w l ls 1, sin(2*x) w l ls 2, 
sin(3*x) w l ls 3, sin(4*x) w l ls 4, 
cos(  x) w l ls 5, cos(2*x) w l ls 6, 
cos(3*x) w l ls 7, cos(4*x) w l ls 8

Maybe you can use more line-kinds by changing the line-type (short
dashed, long dashed, etc), but the other lines except for
those 4 types are hard to
recognize. You should avoid to use several kinds of thickness, because
they are indistinguishable in a small figure.

The maximal number of line kinds may depend on your figure
appearance. Practically, a figure that includes more than 10 lines
is impossible. If you really need to use such a many kinds of
lines, you should use colors.

“Lines with Symbols” means to draw a line first, and symbols are
overlayed on it in order to distinguish each line. The symbols you
can use are circles, triangles, squares, and so on.

gnuplot> set linestyle 1 lt 1 lw 3 pt 5
gnuplot> set linestyle 2 lt 1 lw 3 pt 6

The linestyles are defined above, and they are used at plotting
plot sin(x) w linespoints ls 1.
With this method it is sometimes difficult to
control an interval of each symbol. When you plot a figure in your
datafile, the symbol is placed at the data point, and each data
point is connected by a straight line. In the case of function plot
just like above, those symbols are placed at a fixed interval which
is defined by set sampling .

Write least-squares parameter values in the figure

Make a figure label which tells you a value of parameter obtained at the
least-squares fitting. First, use fit command to get the solution, and
set label "A=%g",a substitutes the value of “a” into the format place
with the specified format.

gnuplot> f(x)=a*x*x+b*x+c
gnuplot> fit f(x) 'test.dat' using 1:2:3 via a,b,c
gnuplot> set label 1 "Y=AX^2+BX+C" at 11,1225
gnuplot> set label 2 "A = %g", a at 12,1200
gnuplot> set label 3 "B = %g", b at 12,1180
gnuplot> set label 4 "C = %g", c at 12,1160
gnuplot> plot f(x),'test.dat' using 1:2:3 with yerr