title: function that finds the cutoff frequency for low pass filter (in matlab)
body: <p>I want to find the cutoff frequency for a lot of low pass filters. Therefor I want a function that can do that for me. I can make a Bode plot and find the frequency for -3dB, but that is boring and time-consuming. Does someone know how I can automatic this procedure? I was trying with </p>
  
  <pre><code>[mag,phase] = bode(sys) 
  </code></pre>
  
  <p>but failed. How should I go about this?</p>
  
  <p>I have filter coefficients <code>a</code>,<code>b</code> available. I try to use some different technique when I discretize the transform function, therefore I want the cutoff frequency empirically from EKV: </p>
  
  <pre><code>y_k = b(1)*x_k + b(2)*x_{k-1} – a(2)*y_{k-1}
  </code></pre>