title: given value of matrix, getting it's coordinate
body: <p>I have matrix, I want to write a function, get the element of matrix and  return me the coordinate of number inside of matrix. could somebody give an idea how to implement it ?</p>
  
  <pre><code>&gt; A
       [,1] [,2]
  [1,]   10   20
  [2,]   21   17
  [3,]   13   25
  [4,]   21   11
  [5,]   31   24
  </code></pre>
  
  <p>for example</p>
  
  <blockquote>
    <p>myfunction(11)</p>
  </blockquote>
  
  <pre><code>&gt; 11
  &gt; row 3, col 1
  </code></pre>