find values within limits

I have the equation of a circle:

(x - a)^2 + (y - b)^2 - r^2 = 0

a, b and r are known values and I would like to find the values of x and y from a predetermined coordinate matrix which satisfies the equation.

example: a = 2, b = 2, r = 2

A = 1 2
      1 3
      2 4
      4 2

The coding to do this is:

a = 2; b = 2; r = 2;
B = A((A(:,1)-a).^2+(A(:,2)-b).^2==r^2,:);

then the last two values would satisfy and hence display 2,4 and 4,2.

What I would like to know is how this code would change if i set limits. Say I want to display only the value that is within the limits of +/-1 for a & b.

i.e. it would only display 2,4

Answer 1

[Image Analyst]

Do you want to create a ring/torus/annulus? If so, see the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_an_ring.3F

[Duncan]

no i don't. what I am doing is related to the distance of a line between 2 points. I have the coordinates of one point and the distance. I just want to find the 2nd coordinate point which matches but within a limit

[Image Analyst]

For a given point, and a distance, there are an infinite number of points. I don't know what the "limit" is - if it's a box bounded by some x,y coordinates, or a sector bounded by some angles, or a point in some arbitrarily shaped region, or whatever. Please upload a diagram that illustrates the situation with an example.

[Duncan]

The "2nd coordinate value" can be found in matrix "A". what i mean by 'limit' is to set a limit on the coordinate points to be displayed that is within matrix A

[Image Analyst]

Maybe I'm just dense but that means nothing to me, but a diagram would help me immensely.