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how to label lines on a graph

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Harold
Harold on 1 Dec 2011
I have a program which asks for variable values of k. A function inputs these into an equation and displays a line on a graph for each value of k. How can i label each of these lines with the value of k used for each. The problem i am having is that the k values are variable and so are the amount of lines displayed on the graph, so i can't figure out how to do this for the values that are fed to the function. Any help would be much appreciated? Thanks, Scott

Answers (8)

Chad Greene
Chad Greene on 10 Aug 2014
label might do the trick.

Matt Tearle
Matt Tearle on 1 Dec 2011
How about overlaying text on the graph, next to the lines?
line(x,y) % or plot(x,y) with a hold on
text(max(x),max(y),num2str(k))
You could play with the (x,y) location of the text. When you say "line" do you mean a straight line or, in general, a curve? The former would make calculating placement very easy; the latter would require some more cleverness, unless max or min works for you.
  3 Comments
Madhuri
Madhuri on 17 Sep 2017
What co ordinates should I specify when I want the text to be on the first point of the curve? text (x(1),y(1), labels) is not working

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Michael
Michael on 1 Dec 2011
The general method would be using the legend function, to which you give a vector of the plot object handles and a series of corresponding strings. For example,
figure; hold on
a1 = plot(x,y1); M1 = "Curve 1";
a2 = plot(x,y2); M2 = "Curve 2";
legend([a1,a2], [M1, M2]);
The legend makes the connection between the plot object a1 and the string M1, and uses this to generate the legend. All you must do in your loop is devise a way to generate ai and Mi for a general integer i. I don't have MATLAB open now to test it but I think there must be a way using a combination of sprintf/num2str:
sprintf('object%s',num2str(a));
Returns "object1" if a=1, "object2" if a=2, etc.,
Hope this helps, though not a complete answer. Mike
  3 Comments
ananya mittal
ananya mittal on 3 Jun 2020
Is there any way of naming around 100 curves in a plot ? This manual way can be very time taking.
Thanks in advance.

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Igor Kubyshkin
Igor Kubyshkin on 26 Feb 2019
function text2line(h,ksi,z,T)
% Inserts text T in/near line with handle h
% ksi - relative distance from the beginning of curve,
% z - shift along normal to curve
%
set(gcf, 'CurrentObject', h)
x=h.XData;
y=h.YData;
i = round(ksi*numel(x));
% Get the local slope
dy=y(i+1)-y(i-1);
dx=x(i+1)-x(i-1);
d = dy/dx;
X = diff(get(gca, 'xlim'));
Y = diff(get(gca, 'ylim'));
p = pbaspect;
a = atan(d*p(2)*X/p(1)/Y)*180/pi;
% Display the text
switch z==0
case 1
text(x(i), y(i), T,'HorizontalAlignment','center', 'BackgroundColor', 'w', 'rotation', a);
case 0
ez=[dy,-dx]/norm([dy,-dx]); % unit normal vector
text(x(i)+z*ez(1), y(i)+z*ez(2), T, 'HorizontalAlignment','center', 'rotation', a);
end
  5 Comments
nlm
nlm on 30 Jul 2020
@ Holden Tranquillo
How did you get this to work ?

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Nathaniel W
Nathaniel W on 8 May 2018
Really late answer, but I was trying to do this same thing earlier. Here's a solution that works, and allows you to use if statments to add additional plots and labels:
t=1:1:10;
x=t;
val=true;
plots = plot(t,x,t,2*x);
names={'x=t','x=2t'};
hold on
if val
plots(end+1)=plot(t,x.*x);
names{end+1}='x=t^2';
end
legend(plots,names)
Credit to this answer for making legend text append work.

Maël Pouget
Maël Pouget on 10 Aug 2021
I know the question is 10 years old, but
plot(curve,'DisplayName','Curve name for the legend')
% or
ax = axes();
hold(ax,'on');
for i = 1:10
plot(i*(1:10),'DisplayName',['Curve #' num2str(i)])
end
hold(ax,'off');
legend();
does the trick (for anyone who, like me, tumbles on this question while trying to name their lines within the plot() call.

Emmanuel Adesina
Emmanuel Adesina on 24 Apr 2021
@Matt Tearle Solution works fine, but puts all labels almost on same line...
line(x,y) % or plot(x,y) with a hold on
if max(y) > 0
text(max(x), max(y), num2str(k))
end
if max(dtm) < 0
text(max(x), min(y), num2str(k))
end
This checks if the plot is positive or negative and places the label accordingly
If you set both as min, it will place it at the origin of the line.
I hope there's a means to set it at the mid-point or other coordinates on the line.

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