Logarithmic colorbar for multiple colored plots


I have a series of plots, each associated with a different value of a parameter called k. The idea was to plot each line with a different color from a colormap and have the colorbar indicate which value of k each plot is associated with, rather than using a legend. The plots are created by a loop, creating one plot per iteration.

I’m quite happy I found the parameter line_z, which automatically creates a colorbar and assigns the right color to the plot, rather than having to create both of them seperately, as suggested in some places on the internet.

However, the parameter k is exponentially spaced (from 5 to 500, so 50 is the midpoint) so I need logarithmic scaling.

colorbar_scale=:log10 seems to do that for the colorbar just fine, but the plots don’t follow, so the colors don’t match. I suppose one option would be to take the log of k instead and change the tick labels, but I haven’t figured out how to change tick labels and that also seems like an ugly workaround for something that should work out of the box. Setting zscale=:log10 just prints a warning No strict ticks found.

I’m using this before the loop:

using Plots
plot(xlabel="\$L_v\$ (pu)", ylabel="frequency (Hz)", colorbar_title="k")

This at the end of the loop

plot!(x, y, seriescolor=:roma, line_z = k, label="", colorbar_scale=:log10)

and somehow I still need to run plot!() after the loop for the plot to actually show up, I’m not quite sure why.
This is without the parameter colorbar_scale, plot colors and colorbar locations match, but you can’t tell the first 2 plots apart, because they have almost the same color:

This is with the parameter colorbar_scale, the colorbar looks fine, but the plots don’t look any different and thus no longer match the values indicated by the colorbar

Taking the log10 of k gives me correct plot colors, but the colorbar scale if obviously wrong:

I was thinking I could use the latter and modify the tick labels, but I haven’t figured out how to do that and I also think that I should not need to do this - the correct color scaling should work out of the box.

My problem seems very similar to what is discussed in this issue, but it says the issue is solved and I don’t really know how to transfer the workarounds to my problem without major changes to the plotting code.

The link provided suggests the issue is solved in CairoMakie and PythonPlot, but not in Plots?

Yeah, that seems to be the case, also the issue is filed with Makie. I’m still a bit confused about the different Plotting options in Julia. Should I file an issue with Plots?

There is probably already an issue about this in Plots.jl, but please do some searching before opening a new one.

It affects the gr() backend, but not e.g. pythonplot().

Simple test code:

using Plots; pythonplot(dpi=100)

x = [0, 1]
y = [i*x for i in 1:5]
z = [10^i for i in 1:5]

p = plot()
foreach(i->plot!(x, y[i], c=:jet, line_z=z[i], label="", colorbar_scale=:log10), 1:5)

Not if we define the plot keyword argument colorbar_title as: colorbar_title="log10(k)"