How can I remove unwanted noise data., shown at the right of the red line

Is there any function that is able to solve the problem?

Answer 1

[Hiro Yoshino]

1. Define the line as a function f
2. Given (x,y), delete the point if f(x) < y satisfies

% data
X = rand(100,2);
x = X(:,1);
y=X(:,2);
plot(x,y,'o'); hold on
% function
f = @(x) x.^2;
x2 = sort(x);
y2=sort(f(x));
plot(x2,y2); hold off

% Find the data poits that satisfies f(x) > y
idx = f(x) > y;
plot(x(idx),y(idx),'o',x2,y2,'r-');