MATLAB: Plotting Chart With 2 X Axes and 2 Y Axes

axessemilogx

Hi there,
I am trying to plot various curves using semilogx along with the line of best fit. I also want to plot some other plots of semilogx on different axes (but in the same figure). I have:
ARI = ones(n,1)./P; % Average Return Interval 1/P
semilogx((ARI), Q);
p_1 = polyfit(log(ARI),Q,1); % Linear best fit
f_1 = polyval(p_1,log(ARI));
hold on
ax1 = gca; % Axis for Linear Fit
ax1.XColor = 'r';
ax1.YColor = 'r';
ax1_pos = ax1.Position; % Position of first axes
ax2 = axes('Position', ax1_pos, 'XAxisLocation','top','YAxisLocation',"right",'Color', 'none'); % Create the second axis
semilogx(ARI, f_1,  '--r');
Q_100yr = polyval(p_1, log(100)) % Q value for 1 in 100 year
hold off
For some reason when I try to create the second axis, the position of the axis is not as I would like and I lose my original log curve. It ends up looking like this:
Could someone help me to get the 2 axes working.
Thanks in advance,
Brian

Best Answer

In the example plot provided in the question, the x axis is the same for both pairs of axes. To use a left and right axes with the same x axis, se yyaxis.
ARI = ones(n,1)./P; % Average Return Interval 1/P
yyaxis left
semilogx((ARI), Q);
yyaxis right
p_1 = polyfit(log(ARI),Q,1); % Linear best fit
f_1 = polyval(p_1,log(ARI));
semilogx(ARI, f_1,  '--r');
Q_100yr = polyval(p_1, log(100)) % Q value for 1 in 100 year
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