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# NullPotential.py: class that implements a constant potential
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from .Potential import Potential
[docs]class NullPotential(Potential):
"""Class that implements a constant potential with, thus, zero forces. Can be used, for example, for integrating orbits in the absence of forces or for adjusting the value of the total gravitational potential, say, at infinity"""
normalize= property() # turn off normalize
[docs] def __init__(self,amp=1.,ro=None,vo=None):
"""
NAME:
__init__
PURPOSE:
initialize a null potential: a constant potential with, thus, zero forces
INPUT:
amp - constant value of the potential (default: 1); can be a Quantity with units of velocity-squared
ro=, vo= distance and velocity scales for translation into internal units (default from configuration file)
OUTPUT:
(none)
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
Potential.__init__(self,amp=amp,ro=ro,vo=vo,amp_units='velocity2')
self.hasC= True
self.hasC_dxdv= True
self.hasC_dens= True
return None
def _evaluate(self,R,z,phi=0.,t=0.):
"""
NAME:
_evaluate
PURPOSE:
evaluate the potential at R,z
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
Phi(R,z)
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 1.
def _Rforce(self,R,z,phi=0.,t=0.):
"""
NAME:
_Rforce
PURPOSE:
evaluate the radial force for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
the radial force
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
def _zforce(self,R,z,phi=0.,t=0.):
"""
NAME:
_zforce
PURPOSE:
evaluate the vertical force for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
the vertical force
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
def _dens(self,R,z,phi=0.,t=0.):
"""
NAME:
_dens
PURPOSE:
evaluate the density for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
the density
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
def _R2deriv(self,R,z,phi=0.,t=0.):
"""
NAME:
_R2deriv
PURPOSE:
evaluate the second radial derivative for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
the second radial derivative
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
def _z2deriv(self,R,z,phi=0.,t=0.):
"""
NAME:
_z2deriv
PURPOSE:
evaluate the second vertical derivative for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
the second vertical derivative
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
def _Rzderiv(self,R,z,phi=0.,t=0.):
"""
NAME:
_Rzderiv
PURPOSE:
evaluate the mixed R,z derivative for this potential
INPUT:
R - Galactocentric cylindrical radius
z - vertical height
phi - azimuth
t - time
OUTPUT:
d2Phi/dR/dz
HISTORY:
2022-03-18 - Written - Bovy (UofT)
"""
return 0.
