code: public static void changeSign( DMatrixD1 a )
      {
          final int size = a.getNumElements();
  
          for( int i = 0; i < size; i++ ) {
              a.data[i] = -a.data[i];
          }
      }
docs: <p>
  Changes the sign of every element in the matrix.<br>
  <br>
  a<sub>ij</sub> = -a<sub>ij</sub>
  </p>
  
  @param a A matrix. Modified.