How to extrapolate airfoil trailing edge to make it closed?

Hi everyone.

I am working on airfoils right now. When l plot the data, airfoil trailing edge comes open. l tried the accepted answer on this link ( https://www.mathworks.com/matlabcentral/answers/279331-extrapolation-and-estimation-of-data ), but it didn't work for me (gives unrelated negative values). Can anyone help me to solve this problem?

[Ayush Anand]

Could you maybe attach your plot and the exact code you have used? I am getting the correct plot with the code given in the answer

[piston_pim_offset]

The code was like this:

data = xlsread('data.xlsx'); % Airfoil data
extr = linspace(1,0.9,100);
data_extr = interp1( data(:,1) , data(:,2) , extr ); % Extrapolation of trailing edge

plot(data(:,1) , data(:,2) , 'r') % Plot of airfoil from original data
hold on
plot(extr , data_extr , 'k') % Plot of trailing edge

[Ayush Anand]

I can't reproduce the results without the actual data you are importing from "data.xlsx". If its not private data, would you mind sharing that as well?