GPS Command Example 30:

# 1D accelerator beam
#
/gps/particle proton
/gps/pos/type Beam
#
# the incident surface is in the y-z plane
/gps/pos/rot1 0 1 0
/gps/pos/rot2 0 0 1
#
# the beam spot is centered at the origin and is
# of 1d gaussian shape with a 3mm central plateau
/gps/pos/shape Circle
/gps/pos/centre 0. 0. 0. mm
/gps/pos/radius 3. mm
/gps/pos/sigma_r .2 mm
#
# the beam is travelling along the x-axis with 5 degrees dispersion
/gps/ang/rot1 0 0 1
/gps/ang/rot2 0 1 0
/gps/ang/type beam1d
/gps/ang/sigma_r 5. deg
#
# the beam energy is in gaussian profile centered at 400 MeV
/gps/ene/type Gauss
/gps/ene/mono 400 MeV
/gps/ene/sigma 50. MeV

Resulted Distribution Plots: