How to find data points within 2% tolerance of curve

Suppose, I have any curve , assume y=x^2 . And I have some scatter data points(X,Y) . Then , how to find scattter data points which are in 2% tolerance of curve y=x^2.

Answer 1

[Chad Greene]

Sounds like a nice homework problem.

You'll probably want to use logical indexing to find the indices of the Y data that are within some range of your predicted y curve.

If you wanted to find the indices of all Y values that are greater than 3 and less than 5, you'd do

ind = y>3 & y<5; 

which would return true for all of the y values that are within that range.

Now try the same logic, but find the indices of all Y points that are greater than 0.98 of your x^2 curve, and less than 1.02.

[Chad Greene]

Here's an example.

X = 1:100; 
Y = 10*rand(100,1); 
plot(X,Y,'.','color',0.8*[1 1 1])

Now the indices of all the Y data between 3 and 5:

ind = Y>3 & Y<5; 
hold on
plot(X(ind),Y(ind),'ro')