Classically, this equation describes the dynamics of a spin in a magnetic field. An ideal magnet consists of a collection of identical spins behaving independently, and thus the total magnetization M → {\displaystyle {\vec {M}}} is proportional to the Bloch vector R → {\displaystyle {\vec {R}}} . All that is left to obtain the final form of the optical Bloch equations is the inclusion of the phenomenological relaxation terms.