title: Finding the maximum absolute value whilst preserving + or - symbol
body: <p>If I have a matrix:</p>
  
  <pre><code>mat=matrix(c(-21,14,28,17,-16,-9,-17,-30,18), nrow=3)
  mat
            [,1]   [,2]  [,3]
       [1,]  -21     17    17
       [2,]   14    -16   -30
       [3,]   28     -9    18
  </code></pre>
  
  <p>I can isolate the highest absolute value simply with</p>
  
  <pre><code>max(abs(mat))
  </code></pre>
  
  <p>However how do I preserve the sign so I return -30? 
  For some context, I have a large number of matrices and I need a command to isolate the highest absolute number in all of them including the sign (some will be positive others negative).</p>
  
  <p>Thanks in advance! </p>