title: Finding indices of multiple items in a matrix?
body: <p>I have an array of elements and I want to see the indices of them inside another matrix</p>
  
  <p>For example, for</p>
  
  <pre><code>A = [1 2 3] 
  B = [1 2 3 4 5 3 4 5 1 2 3]
  </code></pre>
  
  <p>then result array </p>
  
  <pre><code>C = [1 2 3 6 9 10 11] 
  </code></pre>
  
  <p>that give the indices of 1 2 3</p>
  
  <p>Is there any function or a short way to handle?</p>