How to create a quadrant-circle shape-matrix in Matlab?

Question

Currently I have a problem with creating a matrix with a quadrant-shape. The problem is as follow:

I would like to have a 138 x 140 matrix with values of 2 and 3. Inside and on the quadrant circle, the values should be 2. Everything outside the circle, I need to have a value of 3. The radius of the circle is 138 (=R138). Hopefully the image below will support my explanation.

I was thinking of using 'triu' (and then flip) in matlab: then I will not get a circle, but a triangle instead (have not tried it yet). And that is not what I want.

What is the simplest way to create this matrix?

Answer 1

You could try this:

a = ones(138, 140)*3;
[gx, gy] = meshgrid(139:-1:0, 137:-1:0);
a(gx.*gx + gy.*gy <= 138*138) = 2;