title: Iteratively-defined Numpy Array Creation
body: <p>I'm having trouble phrasing this problem in Numpy.  I need to simulate an analog maximum tracker (resistor diode capacitor).  I have some very long 1-D array X from which I want to calculate the output array Y, such that</p>
  
  <pre><code>Y[0] = X[0]
  Y[i] = max(0.99 * Y[i - 1], X[i])
  </code></pre>
  
  <p>I've faked it by approximating my above rules with <code>Y^30 = ExpDecayFunc * X^30</code> where the asteriks is convolution.  Surely there is something much more straight forward I'm missing?  Thanks so much!</p>