Equally spaced markers in a loglog plot

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Hello,
I have the following problem: I am plotting a line in a loglog plot. However since the figure will be printed in black&white I want additional markers to be on the line. Is there a simple way to have the makers equally spaced in the loglog scale. The way I am doing it right now is:
x=linspace(1000,10000,1000);
data=x.^-0.5;
loglog(x,data)
hold on
scatter(x(1:100:end),data(1:100:end));
But obviously this makes the marker not equally spaced. I could make a function for 'data' and than feed it with the right values,like this:
xx=(10*ones(1,11)).^(3:0.1:4);
data_fun=@(a) a.^-0.5;
figure()
loglog(x,data)
hold on
scatter(xx,data_fun(xx));
but I was wondering if there is a simpler way, since that would mean creating a lot of functions (in my case). Thx Vali

Accepted Answer

Chad Greene
Chad Greene on 13 Oct 2014
Edited: Chad Greene on 13 Oct 2014
x=linspace(1000,10000,1000);
data=x.^-0.5;
loglog(x,data)
hold on
evenMarkers(x,data,11);
where evenMarkers is this function:
function [xmarkers,ymarkers,h] = evenMarkers(x,y,NumMarkers)
xmarkers = logspace(log10(x(1)),log10(x(end)),NumMarkers);
ymarkers = interp1(x,y,xmarkers);
h = plot(xmarkers,ymarkers,'ko');
end
  2 Comments
Vali
Vali on 13 Oct 2014
seems like a very elegant solution. I will use that.
Thank you Chad!
Matthew
Matthew on 8 May 2019
Excellent solution Chad, but I am going to suggest a small improvement. If plotting linearly spaced data on a loglog plot, say the results from a fft of a time signal, the distance between points at low frequencies can be quite large. Doing the fit in linear space causes an issue here because a line in linear space is not a line in log space. So I recommend the following adjustment:
function [xmarkers,ymarkers] = evenMarkers(x,y,NumMarkers)
xmarkers = logspace(log10(x(1)),log10(x(end)),NumMarkers);
ymarkers = interp1(log10(x),log10(y),log10(xmarkers));
ymarkers = 10.^(ymarkers);
end

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More Answers (1)

Chad Greene
Chad Greene on 13 Oct 2014
You can use logspace. :)
  1 Comment
Vali
Vali on 13 Oct 2014
logspace is a nice function to help creating the variable xx so instead of
xx=(10*ones(1,11)).^(3:0.1:4);
I can do
xx=logspace(3,4,10)
but that still does not solve the problem of plotting the markers, at least I don't understand how.

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