重写作为C++绑定的系统的动力学

Question

我试图加载一个系统，然后覆盖它的动力学，这样像Simulator这样的类就可以使用新的动力学了。这对于用python声明的系统来说很简单，但对于C++绑定的系统似乎不起作用——例如，下面的示例：

from pydrake.all import DirectCollocation, Simulator, VectorSystem
from pydrake.examples.pendulum import PendulumPlant
import numpy as np

class CustomVectorSystem(VectorSystem):
def __init__(self):
VectorSystem.__init__(self, 1, 0)
self.DeclareContinuousState(2)
def DoCalcVectorTimeDerivatives(self, context, u, x, x_dot):
x_dot[0] += u

class OverwrittenVectorSystem(CustomVectorSystem):
def __init__(self):
CustomVectorSystem.__init__(self)
def DoCalcVectorTimeDerivatives(self, context, u, x, x_dot):
x_dot = np.zeros_like(x_dot)

class OverwrittenPendulumPlant(PendulumPlant):
def __init__(self):
PendulumPlant.__init__(self)
def DoCalcTimeDerivatives(self, context, derivatives):
derivatives = np.zeros_like(derivatives)

def run_sim_step(sys, t=0.1):
context = sys.CreateDefaultContext()
simulator = Simulator(sys)
context = simulator.get_mutable_context()
context.SetContinuousState([0, 1])
context.FixInputPort(index=0, data=[1.0])
simulator.AdvanceTo(t)
return context.get_continuous_state_vector().get_value()

vector_sys = CustomVectorSystem()
overwritten_vector_sys = OverwrittenVectorSystem()
print(
"CustomVectorSystem results are {}, and {} for overwrite".format(
run_sim_step(vector_sys), run_sim_step(overwritten_vector_sys)
)
)
pendulum = PendulumPlant()
overwritten_pendulum = OverwrittenPendulumPlant()
print(
"PendulumPlant results are {}, and {} for overwrite".format(
run_sim_step(pendulum), run_sim_step(overwritten_pendulum)
)
)

返回以下内容：

CustomVectorSystem results are [1.4075 1.    ], and [0. 1.] for overwrite
PendulumPlant results are [0.11427129 1.24633296], and [0.11427129 1.24633296] for overwrite

离散系统也是如此。在这种情况下，有没有办法找到一种新的方法来覆盖动力学？

Answer 1

这是我所期望的行为——允许过载的C++系统在pybind11层中有一些特殊的"蹦床"逻辑。但这也不是我预想的工作流程。你真的在尝试使用PendulumPlant或其他基类吗？VectorSystem过载真的那么糟糕吗？

请注意，即使在C++中，PendulumPlant也被标记为final，我们也不希望用户从中派生。