# How to add some fluctuation in the flat line?

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Nisar Ahmed on 4 Nov 2021
Commented: Jon on 8 Nov 2021
Hi,
In the upper part of attached/copied figure, the encircled area, the graph has values equal to one (straight/flate line). Suppose I want add some fluctuation in the flat line such that numerical values remain in between 0.96 -0.99.
Is there any way I can do in Matlab? Please guide me in this regard. Jon on 4 Nov 2021
Edited: Jon on 4 Nov 2021
I think you can adapt the approach that I illustrate here:
% generate original function with flat zone
t = linspace(1970,1880);
x = zeros(size(t));
% use logical indexing to work on specific portions of curve
x(t<1918) = 1;
x(t>1918) = 0.5+0.1*randn(size(x(t>1918)));
% plot original curve
figure,plot(x,t)
% make the early years noisy too
sigma = 0.015;
xbar = (0.96+0.99)/2;
x(t<1918) = xbar + sigma*randn(size(x(t<1918)));
figure,plot(x,t)
My y axis (years?) is increasing rather than decreasing like yours. This is the normal way to make an x-y plot. I'm not sure if this is important to you. I mostly just wanted to illustrate how you add the noise to a selected portion of your graph.  Jon on 8 Nov 2021
Glad to hear. Good luck with your project