code: public static void changeSign( DMatrix4x4 a )
      {
          a.a11 = -a.a11; a.a12 = -a.a12; a.a13 = -a.a13; a.a14 = -a.a14;
          a.a21 = -a.a21; a.a22 = -a.a22; a.a23 = -a.a23; a.a24 = -a.a24;
          a.a31 = -a.a31; a.a32 = -a.a32; a.a33 = -a.a33; a.a34 = -a.a34;
          a.a41 = -a.a41; a.a42 = -a.a42; a.a43 = -a.a43; a.a44 = -a.a44;
      }
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.