[NOR]
Metropolis update.

[R]
Usual heatbath update
phi'_x = sqrt(ln( 1/(1-r) )) * ( cos(theta) + i sin(theta) ) / sqrt(M) + V_x / M ,
with r chosen randomly in [0,1] and theta chosen randomly in [0,2M_PI].

[R+]
R + overrelaxation.

[1MR]
Same as R, but with r = 1 - r_old instead of choosing r randomly in [0,1].

[1MR+]
1MR + overrelaxation.