How to flip the top x-axis so it matches the bottom plot?

Hello,

I'm trying to plot a power spectra map with two x-axes. The bottom x-axis should be frequency and the top x-axis should be wavelength. Is there any way to match the x-axes so they match since the two variables are not directly proportional (Frequency = 1/Wavelength)?

Here is my code:

figure(666)
% setup bottom axis
ax = axes();
hold(ax);
ax.XAxis.Scale = 'log';
xlabel(ax, 'Frequency', 'Interpreter', 'latex', 'FontSize', 14);
ylabel(ax, 'Power', 'Interpreter', 'latex', 'FontSize', 14);

ax_top = axes(); 
hold(ax_top);
ax_top.XAxisLocation = 'top';
ax_top.YAxisLocation = "right";
ax_top.YTick = [];

ax_top.Color = 'none';
xlabel(ax_top, 'Wavelength', 'Interpreter', 'latex', 'FontSize', 14);

linkprop([ax, ax_top],{'Units','Position','ActivePositionProperty'});

ax.XLim = [0.01 0.5];
ax_top.XLim=[0 50];;
ax_top.XAxis.MinorTick = 'off';
semilogx(ax, F, Spec, '-k', 'LineWidth', 3); hold on 
plot(ax_top,L,Spec,'-k','LineWidth',2); hold on
xline(ax,fs(1),'-r','LineWidth',2); hold off
legend('Power Spectrum','','Speration Frequency')

And here is my resulting plot

I also attached my data if you would like to use it.

Answer 1

[Star Strider]

I am not certain what you want.

One option —

ax_top.XAxis.TickLabels = 1./(ax_top.XAxis.TickValues); % <— ADDED

That takes the current top x-tick values, keeps them as they are, and simply labels them as the inverses of the current values.

LD = load(websave('Data','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1164788/Data.mat'));

F = LD.F;
L = LD.L;
Spec = LD.Spec;
fs = LD.fs;

figure(666)
% setup bottom axis
ax = axes();
hold(ax);

Current plot held

ax.XAxis.Scale = 'log';
xlabel(ax, 'Frequency', 'Interpreter', 'latex', 'FontSize', 14);
ylabel(ax, 'Power', 'Interpreter', 'latex', 'FontSize', 14);

ax_top = axes(); 
hold(ax_top);

Current plot held

ax_top.XAxisLocation = 'top';
ax_top.YAxisLocation = "right";
ax_top.YTick = [];

ax_top.Color = 'none';
xlabel(ax_top, 'Wavelength', 'Interpreter', 'latex', 'FontSize', 14);

linkprop([ax, ax_top],{'Units','Position','ActivePositionProperty'});

ax.XLim = [0.01 0.5];
ax_top.XLim=[0 50];;
ax_top.XAxis.MinorTick = 'off';
% getax_top = get(ax_top)
ax_top.XAxis.TickLabels = 1./(ax_top.XAxis.TickValues);             % <— ADDED
semilogx(ax, F, Spec, '-k', 'LineWidth', 3); hold on 
plot(ax_top,L,Spec,'-k','LineWidth',2); hold on
xline(ax,fs(1),'-r','LineWidth',2); hold off
legend('Power Spectrum','','Speration Frequency')

Warning: Ignoring extra legend entries.

.

Answer 2

[Image Analyst]

Not sure what you want but try using one of these after you've made the plot

axis ij
axis xy