Neimark D-partition method

Hi, Maybe, someone will have advice for me. I am making PID regulator and use Neimark D-partition method, because in my opinion it is easy. But i have problem, because I don't know how need to draw D-curve. Maybe is special function in matlab, which draw D-curve.

My code is:

    sys=tf([-88],[1 0 -6540]);
    w=[0:0.001:100];
    phase_margin=30;
    k=-((w.*j).^2-6540)./((-88)*exp(-phase_margin*j));
    ki=-(((w.*j).^2-6540).*w.*j)./((-88)*exp(-phase_margin*j));

And I don't know how need to write futher code, which will draw D-curve. I tryed to use plot() function, But my attempt was not successful.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup