PCSE 自带的示例代码 14 的解释01
解释代码：%%writefile gddmodel.py
这段代码使用 Jupyter Notebook 的魔法命令 %%writefile 将代码写入一个名为 gddmodel.py 的 Python 文件中。该文件定义了一个简单的模型，用于累积作物生长周期内的生长度日（Growing Degree Days, GDD）。以下是对代码的详细解释：
1. 导入必要的模块
# Here we import some components from PCSE that are building blocks for# any model in PCSE.from pcse.base import SimulationObject, StatesTemplate, RatesTemplate, ParamTemplatefrom pcse.traitlets import FloatSimulationObject：所有 PCSE 模型的基本类。StatesTemplate：用于定义状态变量的模板。RatesTemplate：用于定义变化率变量的模板。ParamTemplate：用于定义参数的模板。Float：用于定义浮点数类型的参数。
2. 定义模型类
# Models in PCSE always inherit from SimulationObjectclassGrowingDegreeDayModel(SimulationObject):"""A simple model to accumulate growing degree days between start and end of the crop cycle. """GrowingDegreeDayModel类继承自SimulationObject，这是所有 PCSE 模型的基本要求。
3. 定义参数
# This defines the model parameters. It inherits from ParamTemplate, this ensures that parameters# receive their value and it signals when parameters are missing.classParameters(ParamTemplate): BaseTemperature = FloatParameters类继承自ParamTemplate，用于定义模型的参数。BaseTemperature：定义了基温，这是一个浮点数类型的参数。
4. 定义状态变量
# State variables always inherit from StatesTemplate. StatesTemplate provides certain behaviour# such as that state variables must be initialized.classStateVariables(StatesTemplate): GDD = FloatStateVariables类继承自StatesTemplate，用于定义模型的状态变量。GDD：累积的生长度日，这是一个浮点数类型的状态变量。
5. 定义变化率变量
# Rate variables are somewhat similar to states but are initialized automatically to zero.classRateVariables(RatesTemplate): rGDD = FloatRateVariables类继承自RatesTemplate，用于定义模型的变化率变量。rGDD：每日生长度日的变化率，这是一个浮点数类型的变化率变量。
6. 初始化模型
definitialize(self, day, kiosk, parameters):"""Initialize runs only once, when the model is started. It always has three variables: - day: the day when the model starts - kiosk: the VariableKiosk which is an object which is shared between model components - parameters: an object providing the model parameters """# The code below initializes the parameters, state and rate variables.# Note that the initial value of state variable (here: GDD) must be provided. self.params = self.Parameters(parameters) self.states = self.StateVariables(kiosk, GDD=0.0) self.rates = self.RateVariables(kiosk)initialize方法在模型启动时仅运行一次。day：模型开始的日期。kiosk：变量共享对象，用于在模型组件之间共享变量。parameters：提供模型参数的对象。初始化参数、状态变量和变化率变量。注意，状态变量
GDD的初始值必须提供。
7. 计算变化率
defcalc_rates(self, day, drv):"""calc_rates computes the rate of change that occur during the current day. It always has two variables: - the current day (a date) - the driving variables `drv` that contain the meteorological inputs """# Here we compute the increase in GDD and assign it to rate variable rGDD self.rates.rGDD =max(0.0, drv.TEMP - self.params.BaseTemperature)calc_rates方法计算当前天的变化率。day：当前日期。drv：包含气象输入的驱动变量。计算每日生长度日的变化率
rGDD，公式为max(0.0, drv.TEMP - self.params.BaseTemperature)，确保结果非负。
8. 积分变化率到状态变量
defintegrate(self, day, delt):"""This performs the integration of rates of change onto the states. It always has two variables: - the current day - the time step, which is fixed at 1.0 day """# Here we add rGDD multiplied by delt to GDD.# The multiplication with `delt` is mostly for educational purposes (since delt=1.0) although# this may change in the future. self.states.GDD += self.rates.rGDD * deltintegrate方法将变化率积分到状态变量上。day：当前日期。delt：时间步长，固定为 1.0 天。将变化率
rGDD乘以时间步长delt并加到状态变量GDD上。这里的乘法主要是为了教育目的（因为delt固定为 1.0），但将来可能会有所变化。
总结
这个 GrowingDegreeDayModel 类定义了一个简单的模型，用于累积作物生长周期内的生长度日（GDD）。模型通过继承 SimulationObject 类，定义了参数、状态变量和变化率变量，并实现了初始化、计算变化率和积分变化率的方法。通过这些方法，模型可以在每一天更新累积的生长度日。
