log-log plot

I have a log-log graph generated by a specific software. I aim to replicate this graph precisely using MATLAB. I've made an attempt and although I'm getting close, it's not an exact match. The attached (softwarePlot.png) displays the original graph for reference. I'm particularly concerned about emulating the software's x-axis definition and maintaining the uniform spacing between each point. Enclosed is the MATLAB code I've written so far. Additionally, I'm interested in recreating the red line seen in the software's image, which represents the fitted line between the two blue lines.

MATLAB CODE

Q = importdata('data.txt');

figure;

semilogy(Q(:,1), Q(:,2),'og','MarkerSize',5,'MarkerFaceColor', 'g');

desiredXTicks = [0.2 1 5 10 20 40 60 75 90 95 98 99.5]; % Set the desired tick positions

xticks(desiredXTicks);

customXAxisLimits = [2/10,0.98*100]; % Adjust the values as needed

xlim(customXAxisLimits);

hold on

semilogy(Q(:,3),Q(:,4),'-b','linewidth', 1.5)

semilogy(Q(:,3),Q(:,5),'-b','linewidth', 1.5)

semilogy(Q(:,6),Q(:,7),'ok')

hold on

a = Q(:, 3);

a = a(~isnan(a));

b = Q(:, 4);

b = b(~isnan(b));

p = polyfit(Q(:,1),Q(:,2),2)

trend_y = polyval(p, Q(:,1));

plot(Q(:,1), trend_y, '-r','linewidth', 1.5)

legend({'Discharge data','5% lower limit','95% upper limit','Outliers'},'Location','Northwest','fontsize',14)

legend boxoff

ylim([100,1000000]);

The spacing between the values on the x-axis, particularly between 0.2 to 1 and 1 to 5, is too small. I would like these intervals to be larger in the matlab code.

Answer 1

[Sulaymon Eshkabilov]

If understood your posted question, this is how to solve this issue using reverse X-axis data:

Q = importdata('DATA_IN.txt');   % Your data file name is renamed 
figure;
semilogy(Q(:,1), Q(:,2),'og','MarkerSize',5,'MarkerFaceColor', 'g');
desiredXTicks = ([0.2 1 5 10 20 40 60 75 90 95 98 99.5]); % Set the desired tick positions
xticks(desiredXTicks);
customXAxisLimits = ([2/10,0.98*100]); % Adjust the values as needed
xlim(customXAxisLimits);
hold on 
semilogy(Q(:,3),Q(:,4),'-b','linewidth', 1.5)
semilogy(Q(:,3),Q(:,5),'-b','linewidth', 1.5)
semilogy(Q(:,6),Q(:,7),'ok')
hold on
a = Q(:, 3);
a = a(~isnan(a));
b = Q(:, 4);
b = b(~isnan(b));
p = polyfit(Q(:,1),Q(:,2),2);
trend_y = polyval(p, Q(:,1));
plot(Q(:,1), trend_y, '-r','linewidth', 1.5)
legend({'Discharge data','5% lower limit','95% upper limit','Outliers'},'Location','Northwest','fontsize',14)
legend boxoff
ylim([100,1000000]);
set(gca, 'XDir','reverse');
grid on

[Raj Arora]

The plot you attached here is identical to what can be produced from the code I've provided. I've included a .png image for your reference, displaying varying distances for labels on the x-axis (0.2, 1, 5, 10, 20, 40, 60, 75, 90, 95, 95) – this is my intended outcome. Furthermore, the fitted curve corresponds to a line fitted between two blue reference lines, rather than being represented as a scatter plot. (The red color line (in the figure you attached) is the fitted curve for scatter plot not the fitten line exactly between 2 blue lines)