How to find the index of the first repeating value.

I want to find the index of the first repeating value and plot a vertical line at that point, when the graph stabilizes.

a = [1,2,3,4,5,6,7,8,8,8,8,8,8,8,8,8,8,8,8]
b = linspace(0, 10, length(a));

plot(a,b)
%xline(b) exactly at the location where the values repeat in a. 

Answer 1

[Voss]

a = [1,2,3,4,5,6,7,8,8,8,8,8,8,8,8,8,8,8,8];
b = linspace(0, 10, length(a));

% plot(a,b)
plot(b,a)

idx = find(diff(a) == 0, 1)

idx = 8

xline(b(idx))

ylim([0 10])