How to fill the area between two line in a log log plot

Hi,

I want to shade the area between the lower and upper curve. I attached the dat. file so you can use this. The following simple code has been used to generate the given figure.

load limit.dat

a=limit(:,1);

upper=limit(:,2);

lower=limit(:,3);

avg=limit(:,4);

loglog(a,avg,a,upper,a,lower)

Can anybody please come with an idea. Thanks in advance.

Cheers!!

Pavel

Answer 1

[Star Strider]

You need to edit your data to be only those greater than zero (negative and zero values will not plot on a loglog plot anyway, so you lose nothing by eliminating them), then a simple patch call works:

fidi = fopen('Mainul Hoque limit.txt','r');
limitc = textscan(fidi, '%f%f%f%f', 'CollectOutput',1);
limit = limitc{:};

a=limit(:,1);
upper=limit(:,2);
lower=limit(:,3);
avg=limit(:,4);
idx = upper>0 & lower>0 & avg>0;                        % Eliminate Negative & Zero Data

figure(1)
patch([a(idx)' fliplr(a(idx)')], [lower(idx)'  fliplr(upper(idx)')], [0.8 0.8 0.8])
hold on
plot(a(idx),avg(idx), a(idx),upper(idx), a(idx),lower(idx))
hold off
set(gca, 'XScale', 'log', 'YScale','log')

I used a light gray triple [0.8 0.8 0.8] for the fill colour. Use whatever colour works for you.

[Mainul Hoque]

Thanks for your reply.

[Star Strider]

My pleasure.

That was an interesting problem. I learned something from it.

[Samuel diabate]

Hello everyone,

I followed the solution proposed by Star Strider. However I end up with a problem. The patch area isn't filled, just like on this topic https://ch.mathworks.com/matlabcentral/answers/361234-i-am-using-the-patch-function-and-i-am-trying-to-set-a-facecolor-in-2017a-and-nothing-is-working-d. My patch or fill function work just fine normally, they just don't seem to be working correctly for loglolog or semilogs plots. Do you have any solutions ? I tried the solution proposed in that topic I just mentionned, but it didn't work.

Here is my code:

I have 2 subplots here, the second one strictly following what Star Strider suggested. The first one is slightly different, plotting first a blue curve that is forcing the axis to be loglog anyway. In both case i manage to draw the patch, but it is not filled! Only the contour appear!

By the way, there shouldn't be any negative value in my datas.

load('examplecode')
lower=Pxxc(:,1)';
upper=Pxxc(:,2)';

figure
title(['Amplitude : Power Spectrum Content'])

subplot(2,1,1)
loglog(f2,Pxx,'linewidth',1.5);
hold on;
patch([f2', fliplr(f2')],[lower, fliplr(upper)], [0.8 0.8 0.8])
%set(gca, 'XScale', 'log')

xlabel('Period (Years)'); ylabel('Spectral power (normalized)');
flab=get(gca,'xtick'); xlim([1/40 1/2.5]);
set(gca,'xtick', [1/40    1/20    1/10    1/5     1/2.5   ], ...
    'xticklabel',[40      20      10      5       2.5     ]);


subplot(2,1,2)

lower=Pxxc(:,1)';
upper=Pxxc(:,2)';
patch([f2', fliplr(f2')],[lower, fliplr(upper)], [0.8 0.8 0.8])
set(gca, 'XScale', 'log', 'YScale','log')

xlabel('Period (Years)'); ylabel('Spectral power (normalized)');
flab=get(gca,'xtick'); xlim([1/40 1/2.5]);
set(gca,'xtick', [1/40    1/20    1/10    1/5     1/2.5   ], ...
    'xticklabel',[40      20      10      5       2.5     ]);

Thank you for your help!!

Cheers,

Sam

[Star Strider]

For loglog plots, all values of every vector must be > 0.

f2(1) = 1E-5;

The reason is the the log of negative values are pure imaginary, and the log of 0 is -Inf. Only real, finite values plot.

[Samuel diabate]

I focussed on the PSD vector and I didn't think about checking the frequency vector. It works great now, with your help.

Thanks a lot and sorry for the inconvenience.

[Star Strider]

No worries.

A Vote would be appreciated!