我很难理解下面代码中的函数 rhs(u, m, r) 是如何接收参数 m 和 r。从代码中可以看出，函数rhs在函数euler_step(u, rhs, dt)中被调用，但是参数m 和 r 作为参数传递给函数 euler_step，它们也不是全局变量。所以，有人可以向我解释参数 m 和 u 是如何到达函数 rhs 的。
# model parameters:
mpo = 100. # initial mass of the rocket propellant in kg
ms = 50. # mass of the rocket shell in kg
g = 9.81 # gravity in m s^{-2}
rho = 1.091 # average air density in kg/m^{3}
rad = 0.5 # radius of the maximum cross sectional area of the rocket in m
A = numpy.pi*(rad**2)# maximum cross sectional area of the rocket in m^{2}
v_e = 325. # the exhaust speed in m/s
C_D = 0.15 # drag coefficient
rt = 20.0 # propellant burn rate in kg/s
dtp = 5.0 # time interval to empty the propellant in s
### set initial conditions ###
h0 = 0.0 # start at the zero height [m]
v0 = 0.0 # initial speed [m/s]
def rhs(u, m, r):
"""Returns the right-hand side of the phugoid system of equations.
Parameters
----------
u : array of float
array containing the solution at time n.
mp: float
mass of the propellant at time t
mp_rate: float
propellant burn rate
Returns
-------
dudt : array of float
array containing the RHS given u.
"""
print("[m,r]",[m,r])
[h,v] = u.copy()
return numpy.array( [ v, -g + pow((ms+m),-1)*(r*v_e - 0.5*rho*v*abs(v)*A*C_D) ] )
def euler_step(u, rhs, dt):
"""Returns the solution at the next time-step using Euler's method.
Parameters
----------
u : array of float
solution at the previous time-step.
rhs : function
function to compute the right hand-side of the system of equation.
dt : float
time-increment.
Returns
-------
u_n_plus_1 : array of float
approximate solution at the next time step.
"""
return u + dt * rhs(u, m, r)
if __name__ == "__main__":
T = 17.0 # final time
dt = 0.1 # time increment
t = numpy.arange(0.0, T, dt) # time discretization
N = len(t) # number of time-steps
# initialize the array containing the solution for each time-step
u = numpy.zeros((N, 2))
u[0] = numpy.array([h0, v0]) # fill 1st element with initial values
rate = numpy.zeros(N)
mp = numpy.zeros(N)
Np = int(((N)/(T))*dtp) # number of time-steps with propellant burn
rate[0:Np] = rt # propellant burn rate in kg/s
mp[0:Np] = mpo - rt*t[0:Np]
# time loop - Euler method
for n in range(1,N-1):
r = rate[n]
m = mp[n]
print("[R,M]",[r,m])
u[n+1] = euler_step(u[n], rhs, dt)
提前致谢。
请您参考如下方法:
m 和 n 是全局变量。
这可能会造成混淆，因为它可能看起来 __main__ 是一个函数，但实际上不是。 if __name__ == "__main__".... 在全局范围内运行。
