Cfrgtkky

Is it possible to plot a graph using different scale for negative and positive values in y-axes in Gnuplot?

I want to set the y range of the values in the y-axes from -2 to 70.
For values from 0 to 70 I want a scale e.g. 0,10,20,30,..70.
For values from 0 to -2 I want a different scale: 0, -0.1, -0.2, -0.3,..-2.

Thanks in advance.

Understanding your intention in general, I'm not sure whether the data you are providing are good enough to illustrate your desired outcome, so I have added two more data points where the negative y axis section is actually being used (see at the bottom of the post).

I used

• 
  multiplot to produce two separate plots, one for y values larger and one for those smaller than zero


• the ternary operator (a ? b : c) to separate the date for each plot

I have done no work on the resulting graph, so it is extremely basic, and the large point size and different shape is only to "make the point". This is not a solution but should get you started:

# set up multiplot so that the two subgraphs are joined

set multiplot layout 2,1 margins 0.1,0.95,0.1,0.95 spacing 0

# no titles please

unset key

# we don't want tics for the upper half

unset xtics



plot[-2:2][0:70] "so.dat" using 2:($3>0?$3:NaN)

                 w points pt 7 ps 2



# we do want xtics at the bottom

set xtics

plot[-2:2][-2:0] "so.dat" using 2:($3<0?$3:NaN)

                 w points pt 5 ps 2



# cleanup

unset multiplot

reset

yields

My version of the data so.dat:

#                   TCP                     TFO

"Preparation"       1.126717                68.852979 

"Establishment"     -0.0436158              1.5529298

"Transfer"          -0.1172298              0.5735358

"Interruption"      0.125                   -1.25

"Execution"         -1.5                    -0.05

This has an answer already that has been accepted, but I have done some more work that I want to share; in particular,I wanted to have more control over the two subgraphs than the line

set multiplot layout 2,1 margins 0.1,0.95,0.1,0.95 spacing 0

allows. The lower subgraph should be visibly "thinner" than the upper one. Taking the opportunity, I also wanted to address Vladimir's question in his comment. So here we go:

### set up multiplot so that the two subgraphs are joined

set multiplot

 # we need to set a left margin to keep the subgraphs aligned,

 # and we need enough space for the ylabel

set lmargin 10

# no bottom margin, so that the second subgraph touches the upper one

set bmargin 0

# no titles please

unset key

# but we want a ylabel

set ylabel "Scales"

# no xtics

unset xtics

For Vladimir: see help set border

# we want left, top and right 2 + 4 + 8

# but no bottom border

set border 14

Now manually fix the area where we want to draw the first subgraph:

set size 1,0.5                          # full with, half hight

set origin 0,0.5                        # start at the left border, half way up

# optional: colour background

# set object 1 rect from -2,0 to 2,80 fc rgb "yellow" fillstyle solid .15 noborder

Ready to draw the graph:

plot[-2:2][0:80] "so.dat" using 2:($3>0?$3:NaN)

                  w points pt 7 ps 2

The rest in one go:

# we do want xtics a label at the bottom

set xtics -2,.5,2 nomirror

set xlabel "Multiplot In Action"

set ylabel "Different"



set size 1,0.3                  # full width, 30% of height, keep space for xlabel

set origin 0,0.2                # left, keep bottom 20% free

set tmargin 0                   # no top margin, touch the upper subgraph

set bmargin 2                   # for the xlabel

set border 11                   # we want left, bottom and right border, no top 1 + 2 + 8

# set object 2 rect from -2,-2 to 2,0 fc rgb "blue" fillstyle solid .15 noborder

plot[-2:2][-2:0] "so.dat" using 2:($3<0?$3:NaN)

                 w points pt 5 ps 2



# cleanup

unset multiplot

reset

This gives us

I would have liked the colour backgrounds, but the lower one is drawing over the dots in the upper one and I have not been able to fix that (back doesn't help).

Since gnuplot 5.2 you can define nonlinear coordinate systems with set nonlinear. This works similar to set link: You must provide a mapping function and its inverse for the axis you want to change.

In your case, the mapping function would scale all positive y-values and leave the negative ones unscaled:

RATIO=0.1

map(y) = y > 0 ? y*RATIO : y

inv_map(y) = y > 0 ? y/RATIO : y

set nonlinear y via map(y) inverse inv_map(y)



set xrange[-5:50]

plot x