brainpy.analysis.LowDimAnalyzer cannot plot the nullcline that is absolutely horizontal

[c-xy17]

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()