MATLAB: Plotting double bottom x-axis

Question

I'm trying to plot double bottom x-axis according to the figure after the jump:

It is a semilogx-plot in hours with additional specific ticks representing minutes, months and years. How do I create these additional ticks?

Answer 1

You can use Victor May's approach to overlay a secondary axes, but this needs more tweaking to actually work.

First, let's recreate the basic plot:

clear, close
time = [1/60, 1, 24, 24*7, 24*30, 24*30*6, 24*365, 24*365*10];
r = [110, 90, 80, 75, 70, 65, 63, 60];

% plot the data
semilogx(time, r, 'o-')

% adjust ticks and format of primary axes
xlim([0.005 1e6])
ylim([0 140])
tick = 10 .^ (-2 : 6);
set(gca, 'XTick', tick)
set(gca, 'XTickLabel', arrayfun(@num2str, tick, 'UniformOutput', false))
set(gca, 'XMinorTick', 'off')
set(gca, 'TickDir', 'out')

Overlaying a secondary axes only works properly if it has the same position, size, axis limits, and scale type as the primary, and if its background is transparent (otherwise the data become hidden):

% put matching secondary axes on top with transparent background
pos = get(gca, 'Position');
axes('Position', pos)
set(gca, 'Color', 'none')
xlim([0.005 1e6])
ylim([0 140])
set(gca, 'XScale', 'log')
set(gca, 'XMinorTick', 'off')
set(gca, 'TickDir', 'out')

Giving it the proper ticks and tick labels

% adjust ticks
set(gca, 'YTick', [])
set(gca, 'XTick', time)
label = {'1 min', '1 hour', '24 hours', '1 week', '1 month', '6 months', '1 year', '10 years'};
set(gca, 'XTickLabel', label)

results in

– not really what we want.

With a trick we can let the ticks and tick labels of the secondary axes go inside...

% tinker with it
set(gca, 'XAxisLocation', 'top')
pos(4) = eps * pos(4);
set(gca, 'Position', pos)

...but that's still not really what we want.

---

A different strategy: Let's not overlay axes, but put the additional ticks in ourselves!

label = {'1 min', '1 hour', '24 hours', '1 week', '1 month', '6 months', '1 year', '10 years'};
line([time', time'], [0 2], 'Color', 'k')
text(time, 4 * ones(size(time)), label, 'Rotation', 90, 'VerticalAlignment', 'middle')

The result

is still not perfect, but useable.