code: public static void fill( DMatrix2x2 a , double v  ) {
          a.a11 = v; a.a12 = v;
          a.a21 = v; a.a22 = v;
      }
docs: <p>
  Sets every element in the matrix to the specified value.<br>
  <br>
  a<sub>ij</sub> = value
  <p>
  
  @param a A matrix whose elements are about to be set. Modified.
  @param v The value each element will have.