MATLAB: How to plot a semi-circle

Question

How to plot a semi-circle and if I want just the curve of of the semi-circle and the radius of the circle is 500m?

Thanks

Answer 1

      theta = 0:.01:pi;
      y = 500*exp(1j*theta);
      plot(real(y),imag(y));
      axis([-750 750 -750 750]);
      grid on;