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1

how to set a marker at one specific point on a plot (look at the picture)?

Asked by benjamin ma on 27 Feb 2014
Latest activity Commented on by MathWorks Support Team on 27 Nov 2018

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3 Answers

Answer by Mischa Kim
on 27 Feb 2014
Edited by Mischa Kim
on 27 Feb 2014
 Accepted Answer

Benjamin, add
hold on
plot(x_pos,y_pos,'r*')
to your code. (x_pos,y_pos) is the data point that needs to be marked. So if you have
x = 0:0.1:pi;
y = sin(x);
you could use
plot(x,y)
hold on
plot(x(10),y(10),'r*') % marking the 10th data point of x and y

  2 Comments

Thank you. it works now. but one question, can i use "set" function to mark a plot also?
Sure. First you will need to define the plot object, however. Something like this should work:
h = plot(NaN, NaN, 'r*'); %define the graphics object, but don't render anything.
set(h,'Xdata', x(10), 'YData', y(10)); %mark 10th point
pause(5); %after a few seconds...
set(h, 'XData', x(20), 'YData', y(20)); %mark 20th point instead.

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Answer by Greg
on 6 Dec 2017
Edited by Greg
on 6 Dec 2017

With 7k views in a month, I'm surprised this hasn't been updated.
Starting in R2016b, there is a MarkerIndices property. Instead of the other answer's suggested:
plot(x,y);
hold on;
plot(x(10),y(10),'r*');
Now simply use:
h = plot(x,y,'MarkerIndices',10);
Move the marker(s) around at any time if you've stored the handle h:
h.MarkerIndices = 5:5:length(x);

  1 Comment

In addition, you can specify the ‘o-‘ line style, which creates a solid line and markers. You can also specify marker properties, such as the face color and edge color.
x = linspace(0,pi,30);
y = sin(x);
p = plot(x,y,'o-','MarkerFaceColor','red','MarkerEdgeColor','red','MarkerIndices',10)

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Answer by navi g
on 9 Jan 2017

hello, is this marking in plot is possible without writing code, and putting mark in plot in figure editor,
and for sinosoidal curve i have only x data, i dont have y data, but i need to mark on curve, means that i will give x value, based on x value it should place on curve exactly on sinosoidal curve,

  1 Comment

For R2014b or later (I would have to check about earlier; I see some references in 2012 time frame) you can use data brushing. Click on the paintbrush in the figure and then you can click on a point to mark it.
For marking a particular location given only the x, then
x_to_mark = SomeSpecificXValue;
all_lines = findobj(gca, 'type', 'line');
number_of_marks = 0;
where_to_mark = [];
for K = 1 : length(all_lines)
this_line = all_lines(K);
this_xdata = get(this_line, 'XData');
if x_to_mark < min(this_xdata) | x_to_mark > max(this_xdata)
continue; %the line does not span that x
end
x_diff = diff(this_xdata);
if isempty(x_diff)
fprintf('skipping line #%d that is single point\n', K);
elseif all(x_diff > 0) | all(x_diff < 0)
%it is monotonic, safe to do interpolation
this_ydata = get(this_line, 'YData');
y_to_mark = interp1(this_xdata, this_ydata, x_to_mark);
number_of_marks = number_of_marks + 1;
where_to_mark(number_of_marks,:) = [x_to_mark, y_to_mark];
else
fprintf('skipping line #%d with unsorted x data\n', K);
end
end
if number_of_marks == 0
fprintf('That x was not found on a line we could handle\n');
else
hold on
plot(where_to_mark(:,1), where_to_mark(:,2), 'r*');
end
This is probably a lot longer than you were expecting. You did not happen to provide information that we might potentially have used to make it shorter. For example if you know there is only exactly one line, and that the x were sorted when you plotted, and that the x value to mark is definitely in range, then the code could be made much shorter.

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