code: def ddRunge(self, x):
      # Runge's second derivative at x
      xx = x * x
      k = 1.0 + 25.0 * float(xx)
      return (-50.0 + 3750.0 * float(xx)) / (k * k * k)
  
file_path: essentia/test/src/unittests/standard/test_cubicspline.py
imports: from essentia_test import *
  from essentia.standard import *
  from numpy import r_, sin, pi
label_desc: Use image node_id 4 for calling the TestCubicSpline obj's underlying member method code with example usage: obj.ddRunge(x) and returns: unknown