code: public static void abs(DMatrixD1 a , DMatrixD1 c ) {
          c.reshape(a.numRows,a.numCols);
  
          final int length = a.getNumElements();
  
          for ( int i = 0; i < length; i++ ) {
              c.data[i] = Math.abs(a.data[i]);
          }
      }
docs: <p>Performs absolute value of a matrix:<br>
  <br>
  c = abs(a)<br>
  c<sub>ij</sub> = abs(a<sub>ij</sub>)
  </p>
  
  @param a A matrix. Not modified.
  @param c A matrix. Modified.