code: public static void add( DMatrix6 a , DMatrix6 b , DMatrix6 c ) {
          c.a1 = a.a1 + b.a1;
          c.a2 = a.a2 + b.a2;
          c.a3 = a.a3 + b.a3;
          c.a4 = a.a4 + b.a4;
          c.a5 = a.a5 + b.a5;
          c.a6 = a.a6 + b.a6;
      }
docs: <p>Performs the following operation:<br>
  <br>
  c = a + b <br>
  c<sub>i</sub> = a<sub>i</sub> + b<sub>i</sub> <br>
  </p>
  
  <p>
  Vector C can be the same instance as Vector A and/or B.
  </p>
  
  @param a A Vector. Not modified.
  @param b A Vector. Not modified.
  @param c A Vector where the results are stored. Modified.