How can I add a second x-axis on top of the matlab figure for the same graph?

I have the following plot on matlab and want to add a second x-axis on top to show the corresponding distances with the same number of ticks and tick labels that can be found by:

distances (m) = (time_tau *10^-9) * 3*10^8

This is the plot:

% delay-spatial domain surf plot
figure
contourf( flip(time_tau), d_up, 20 .* log10(abs(zz_hts_tran_filtered_shift')), 'EdgeColor', 'none')

Unrecognized function or variable 'time_tau'.

set(gca, 'FontSize', 16)
set(gcf, 'color', 'white')
%set(gca, 'YDir', 'reverse')
ylabel('$$\Delta_{\mathrm{\phi}} ~(^\circ)$$', 'Interpreter', 'Latex')
xlabel('$$\tau ~\mathrm{(ns)}$$', 'Interpreter', 'Latex')
zlabel('$$\hat{\sigma}_{\mathrm{eff}}~\mathrm{dB/m^2}$$', 'Interpreter', 'Latex')
xlim([first_limit, last_limit]);
colormap('jet'); % Choose your preferred colormap
colorbar('eastoutside');

[Dyuman Joshi]

There are undefined parameters in the code above, thus we can not run your code.

[demos serghiou]

Here are the files attached

[Dyuman Joshi]

There's still an undefined variable.

Also, can you show what is the expected output/result?

load('time_tau.mat')
load('zz_hts_tran_filtered_shift.mat')
whos

  Name                               Size               Bytes  Class     Attributes

  ans                                1x37                  74  char                
  cmdout                             1x33                  66  char                
  time_tau                           1x1594             12752  double              
  zz_hts_tran_filtered_shift      1594x21              535584  double    complex   

% delay-spatial domain surf plot
figure
contourf( flip(time_tau), d_up, 20 .* log10(abs(zz_hts_tran_filtered_shift')), 'EdgeColor', 'none')

Unrecognized function or variable 'd_up'.

set(gca, 'FontSize', 16)
set(gcf, 'color', 'white')
%set(gca, 'YDir', 'reverse')
ylabel('$$\Delta_{\mathrm{\phi}} ~(^\circ)$$', 'Interpreter', 'Latex')
xlabel('$$\tau ~\mathrm{(ns)}$$', 'Interpreter', 'Latex')
zlabel('$$\hat{\sigma}_{\mathrm{eff}}~\mathrm{dB/m^2}$$', 'Interpreter', 'Latex')
xlim([first_limit, last_limit]);
colormap('jet'); % Choose your preferred colormap
colorbar('eastoutside');

[demos serghiou]

Yes sorry, here is the rest of the variables and output figure.

first_limit = t_total(1) - 1.5;

last_limit = t_total(end) + 2.5;

Answer 1

[Voss]

This creates text objects above the axes at the locations of the x-tick marks for the new x-tick labels, and another text object for the new x-label.

% random data:
time_tau = 1:100;
d_up = 1:10;
zz_hts_tran_filtered_shift = randn(100,10);
first_limit = 20;
last_limit = 65;


% delay-spatial domain surf plot
figure()
contourf( flip(time_tau), d_up, 20 .* log10(abs(zz_hts_tran_filtered_shift')), 'EdgeColor', 'none')
set(gca, 'FontSize', 16)
set(gcf, 'color', 'white')
%set(gca, 'YDir', 'reverse')
ylabel('$$\Delta_{\mathrm{\phi}} ~(^\circ)$$', 'Interpreter', 'Latex')
xlabel('$$\tau ~\mathrm{(ns)}$$', 'Interpreter', 'Latex')
zlabel('$$\hat{\sigma}_{\mathrm{eff}}~\mathrm{dB/m^2}$$', 'Interpreter', 'Latex')
xlim([first_limit, last_limit]);
colormap('jet'); % Choose your preferred colormap
colorbar('eastoutside');


% store some needed things:
ax = gca();
yl = ylim();
xt = xticks();
fs = get(ax,'FontSize');

% decrease the axes height a little, to make room for the new "xlabel"
ax.Position(4) = 0.93*ax.Position(4);

% create tick labels at the top of the plot:
text(xt,yl(2)*ones(numel(xt),1),string((xt *10^-9) * 3*10^8), ...
    'VerticalAlignment','bottom', ...
    'HorizontalAlignment','center', ...
    'FontSize',fs)

% create a new "xlabel":
text(mean(xlim()),yl(2)+0.08*(yl(2)-yl(1)),'distances (m)', ...
    'VerticalAlignment','bottom', ...
    'HorizontalAlignment','center', ...
    'FontSize',fs)

[demos serghiou]

many thanks

[Voss]

You're welcome!