def _rectForce(x,pot,t=0.):
"""
NAME:
_rectForce
PURPOSE:
returns the force in the rectangular frame
INPUT:
x - current position
t - current time
pot - (list of) Potential instance(s)
OUTPUT:
force
HISTORY:
2011-02-02 - Written - Bovy (NYU)
"""
#x is rectangular so calculate R and phi
R= nu.sqrt(x[0]**2.+x[1]**2.)
phi= nu.arccos(x[0]/R)
sinphi= x[1]/R
cosphi= x[0]/R
if x[1] < 0.: phi= 2.*nu.pi-phi
#calculate forces
Rforce= _evaluateRforces(pot,R,x[2],phi=phi,t=t)
phiforce= _evaluatephiforces(pot,R,x[2],phi=phi,t=t)
return nu.array([cosphi*Rforce-1./R*sinphi*phiforce,
sinphi*Rforce+1./R*cosphi*phiforce,
_evaluatezforces(pot,R,x[2],phi=phi,t=t)])
def _FullEOM(y,t,pot):
"""
NAME:
_FullEOM
PURPOSE:
implements the EOM, i.e., the right-hand side of the differential
equation
INPUT:
y - current phase-space position
t - current time
pot - (list of) Potential instance(s)
OUTPUT:
dy/dt
HISTORY:
2010-04-16 - Written - Bovy (NYU)
"""
l2= (y[0]**2.*y[3])**2.
return [y[1],
l2/y[0]**3.+_evaluateRforces(pot,y[0],y[4],phi=y[2],t=t),
y[3],
1./y[0]**2.*(_evaluatephiforces(pot,y[0],y[4],phi=y[2],t=t)
-2.*y[0]*y[1]*y[3]),
y[5],
_evaluatezforces(pot,y[0],y[4],phi=y[2],t=t)]