code: public static void changeSign( DMatrix5x5 a )
      {
          a.a11 = -a.a11; a.a12 = -a.a12; a.a13 = -a.a13; a.a14 = -a.a14; a.a15 = -a.a15;
          a.a21 = -a.a21; a.a22 = -a.a22; a.a23 = -a.a23; a.a24 = -a.a24; a.a25 = -a.a25;
          a.a31 = -a.a31; a.a32 = -a.a32; a.a33 = -a.a33; a.a34 = -a.a34; a.a35 = -a.a35;
          a.a41 = -a.a41; a.a42 = -a.a42; a.a43 = -a.a43; a.a44 = -a.a44; a.a45 = -a.a45;
          a.a51 = -a.a51; a.a52 = -a.a52; a.a53 = -a.a53; a.a54 = -a.a54; a.a55 = -a.a55;
      }
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.