Using matlab to find points on different curves and then join them up

Basically I have created a file which produces a graph with a number of lines on, but need to produce a curve on top. For example, the picture 2nd from bottom on this site shows what im aiming for:

https://www.e-education.psu.edu/png520/m3_p3.html

I have the lines but need to produce the dotted line.

I know the y cooridinates of where the dotted line crosses each other lines, but need to use matlab to find the x coordinates, to plot markers onto the graph and to then join them up with a line.

I've been trying things for ages but am fairly new to matlab.

Would appreciate some help, thankyou!

Answer 1

[Paulo Silva]

%This is how you make a line interactively using left mouse button
%you can see the coordinates of the points on the matlab command line
clf %clear a figure, comment this to plot on a existing figure
clear %clears the variables
axis([0 1 0 1]) %define you axis max and min values [xmin xmax ymin ymax]
hold on %add stuff to the axis without clearing what's there before
for n = 1:2 %choose two points
  [x(n),y(n)] = ginput(1) %waits for you to click on a point on the graph
plot(x(n),y(n),'x') %mark a cross in the point you choose
s=sprintf('Point %d',n); %make the "name" of the point
text(x(n),y(n),s) %insert text Point 1 and after the Point 2
end
line(x,y,'LineStyle','--') %creates a line between two points

%line with diferent atributes from the defaults
%line(x,y,'LineStyle','--',...
%'LineWidth',4,...
%'Color','r') %creates a line between two points

Answer 2

[Jay]

Thankyou. I'll try it in the morning and let you know how it goes! I'm not sure how accurate it will be but i'll try!

[Paulo Silva]

That's just a demo with functions you will need, try them and adjust the code to your needs.

Any doubt about a function just write doc followed by the name of the function in matlab command line, for example

doc line