I don't think there is a way to 'vectorize' this code, you can't eliminate this for loop and achieve much of a speed up. But how about the following:
If rendering the plot is the time-consuming part of your code, you may try generating plot points for all circles into the same X,Y arrays and calling plot() once at the end. Intead of the rectangle function, each circle can be a set of enough number of points which you can calculate using the circle equation.
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