title: Matlab find Series of First Negative Number
body: <p>With a matrix of numbers in Matlab, how would you find the first negative number after a series of positive numbers?  </p>
  
  <p>So far, the only answer I could come up with was to write a loop to check for the first negative number, then record it, then look for the first positive number, and truncate the array there, then start over.  Is there a vectorized way to do this?  </p>
  
  <p>e.g., I have <code>x = [ -1 -5 -2 3 4 8 -2 -3 1 9]</code>, and I want this function or script to give me an array of <code>y = [1 7]</code>.</p>