Find value of x, from max y (graph)

figure(2);
vel = diff(y)./diff(x);
plot(x(1:end-1), vel)

display(max(findpeaks(vel)))
x(max(findpeaks(vel)));

Trying to find the value of x corresponding to the maximum value of y, for this velocity vs time graph.

displays error due to logical or integer access.

Answer 1

[Mischa Kim]

Andrew, check out

 x   = 0:0.1:6;
 y   = sin(x + 0.5);
 vel = diff(y)./diff(x);
 plot(x(1:end-1), vel,x(vel == max(vel)),max(vel),'dr')

Answer 2

[Michael Haderlein]

I'd actually prefer the following:

 ...
 vel = diff(y)./diff(x);
 [maxvel,ind]=max(vel);
 plot(x(1:end-1),vel,x(ind),maxvel,'or')

If you have a large number of velocities, this one here will be faster. For a small number, it just doesn't matter.

[Andrew]

displays the circle, but not displaying the x value still

[Michael Haderlein]

You can just print it in the command window, e.g.

>> x(ind)

ans =

      1.1000

[Andrew]

thank you very much

[Andrew]

in addition, if just have a graph and i wanted to find the x value from a y value, how would i do it ?

[Michael Haderlein]

What do you mean? You can, for instance, use the Data Cursor tool in the menu toolbar. Or you use the handles (plot_handles=get(gca,'children');) of the plots and then extract the x and the y data of the plots (x=get(plot_handles(1),'xdata');).