docstr: Variations on the constructors in the Elements notebook
docstr_tok: ["Variations","on","the","constructors","in","the","Elements","notebook"]
code: def setUp(self):
      "Variations on the constructors in the Elements notebook"
  
      x, y = np.mgrid[-10:10, -10:10] * 0.25
      sine_rings = np.sin(x**2 + y**2) * np.pi + np.pi
      exp_falloff1 = 1 / np.exp((x**2 + y**2) / 8)
      exp_falloff2 = 1 / np.exp((x**2 + y**2) / 9)
  
      self.vfield1 = VectorField([x, y, sine_rings, exp_falloff1])
      self.vfield2 = VectorField([x, y, sine_rings, exp_falloff2])
  
imports: import numpy
  from holoviews import Bars, Curve, Dimension, Histogram, Points, Scatter, VectorField
  from holoviews.element.comparison import ComparisonTestCase
label_desc: Use image node_id 1 for calling the VectorFieldComparisonTest obj's underlying member method code with example usage: obj.setUp() without return types