code: public static void setIdentity( DMatrix3x3 a ) {
          a.a11 = 1; a.a21 = 0; a.a31 = 0;
          a.a12 = 0; a.a22 = 1; a.a32 = 0;
          a.a13 = 0; a.a23 = 0; a.a33 = 1;
      }
docs: Sets all the diagonal elements equal to one and everything else equal to zero.
  If this is a square matrix then it will be an identity matrix.
  
  @param a A matrix.