```python import brainpy as bp bp.math.enable_x64() def ppa2d(group, title, v_range=None, w_range=None, Iext=65., duration=400): v_range = [-70., -40.] if not v_range else v_range w_range = [-10., 50.] if not w_range else w_range # 使用BrainPy中的相平面分析工具 phase_plane_analyzer = bp.analysis.PhasePlane2D( model=group, target_vars={'V': v_range, 'w': w_range}, # 待分析变量 pars_update={'Iext': Iext}, # 需要更新的变量 resolutions=0.05 ) # 画出V, w的零增长曲线 phase_plane_analyzer.plot_nullcline() # 画出固定点 phase_plane_analyzer.plot_fixed_point() # 画出向量场 phase_plane_analyzer.plot_vector_field(plot_style=dict(color='lightgrey', density=1.)) # ... (some codes are not shown) plt.xlim(v_range) plt.ylim(w_range) plt.title(title) plt.show() ``` 