# How to manually move (smoothly) a set of evenly spaced xlines

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Paul Hoffrichter on 18 Nov 2022
Commented: Paul Hoffrichter on 23 Nov 2022
In R2020a on a plot I plan on having a loop to produce 20 xlines that are 200 samples apart. (I know that in later versions, one xline can have an array, but not in R2020a.)
I would like to be able to manually move all of them by some offset < 200, preferably with a mouse. Ideally, I would select the left-most xline with a mouse (or even any point between the first two xlines), and as I move the mouse to the right, all 20 xlines would move smoothly to the right keeping their difference of 200 samples intact. When I let go of the mouse select key, then I would like to know the exact x-coordinate of the left-most xline. (Using the figure tooltip only gives an approximate x-coordinate.) I should then be able to repeat this until I am satisified that all the gaps between the xlines have captured the data symbols correctly.
In following example, I would want to slide the xlines to lie on top of the peaks. (Actual signals are not as clear.)
f = 50*1e6;
phi = 14*pi/9;
t = linspace(0,1,100e3);
y = sin(2*pi*f*t + phi);
plot(y)
for ii = 0:10
xline(ii*200 + 25);
end
xlim( [1 2300] );
I found this question on moving xlines answered by @Steven Lord. Thought that maybe it could help.

Steven Lord on 18 Nov 2022
While you can't create a vector of xline objects in one call in release R2020a, you can store those handles in an array.
axis([-5 5 0 10])
h = gobjects(1, 5);
for k = 1:5
h(k) = xline(k-3); % Lines at -2, -1, 0, 1, and 2
end
Now just update the Value property of each line. A simple for loop would be easiest, but you can change all their properties at once using a one line command if you don't mind it being a little cryptic. This moves the lines to be at positions -3:1.
set(h, {'Value'}, arrayfun(@(obj) obj.Value-1, h, 'UniformOutput', false).')
This uses the "set(H,NameArray,ValueArray)" syntax from the set function's documentation page.
##### 3 CommentsShow 1 older commentHide 1 older comment
Paul Hoffrichter on 21 Nov 2022
Is there a way to grab hold of one of the xlines (e.g., say, the first one), and then slide them slowly and smoothly with the mouse?
Paul Hoffrichter on 23 Nov 2022
Thank you!

Steven Lord on 18 Nov 2022
With your clarifying picture there may be another possibility. You could just put the xline objects in their required position automatically.
x = 0:3600;
y = sind(x);
L = islocalmax(y);
plot(x, y, '-');
hold on
peakLocations = x(L);
for whichpeak = 1:numel(peakLocations)
xline(peakLocations(whichpeak));
end
Another potential approach to highlight the peaks is to add a stem plot.
% stem(x(L), y(L))
##### 3 CommentsShow 1 older commentHide 1 older comment
Steven Lord on 18 Nov 2022
Do you need to perform a visual sanity check or can you programmatically check that the true values returned from islocalmax (and potentially its opposite islocalmin if you're looking for both types of local extrema) are equally spaced?
Paul Hoffrichter on 18 Nov 2022
First I would like to do a visual sanity check.
I work with another group that has a proprietary waveform viewer. They show me how they analyze their data. They use the analogous equal space xlines and use the mouse to slowly move the set of lines to the right or left to analyze their data, and stop when they think their selection makes sense. If 200 samples per symbol is slightly off, they can modify this value in a their text window and all the lines become spaced accordingly. I am trying to emulate parts of their proprietary tool, so that I can perform the same analysis, and if the spacing is a little more or less than 200 samples per symbol (or even a fractional number of samples per symbol), I will be less dependent on that tool.
Once analysis is done and good sanity results are observed from the figures, then I can choose an implementation path with more confidence.
I did use findpeaks and thresholding to identify initial points to throw out. I will explore using islocal[min|max] later.

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