** Next:** 7. Phase Shifts
**Up:** Rotation Matrices and Translation Vectors in
** Previous:** 5. Systematic Absences

The third and last case of special reflections is where **hR** = **h**
and **ht** = 0 (modulo 1). The 2 (or 3 or 4 or 6 or more) contributions
are equally large and have the same phase and thus enlarge each other. The
expected intensity () of such a reflection is 2 (or 3 or 4 or 6 or
more) times as large as that of a general reflection. The factor of enhancement
is called epsilon () and is easily derived as the number of
rotation matrices **R**_{i} that can be applied on **h** and give back
**h**.

*Example* :

In *P*2 there are two symmetry operations:

All reflections of the type (0

**Copyright © 1981, 1998 International Union of
Crystallography**