The dot product is defined as

δ_{i} = ⋅, |
(15.170) |

where *i* is one of {*x*, *y*, *z*},
is a unit vector parallel to the XH bond vector, and
is one of the unit vectors defining the diffusion frame.
The three diffusion frame unit vectors can be expressed using the Euler angles *α*, *β*, and *γ* as

The relax user manual (PDF), created 2016-10-28.