docstr: evaluates Venkataraman's sinc function for a list of coeffs
  
  f(x) = -20 * \sin(r(x))/r(x)
  
  Where:
  r(x) = \sqrt((x_0 - 4)^2 + (x_1 - 4)^2 + 0.1)
  
  Inspect with mystic_model_plotter using::
      mystic.models.venkat91 -b "-10:10:.1, -10:10:.1" -d
  
  The minimum is f(x)=-19.668329370585823 at x=(4.0, 4.0)
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code: def function(self, coeffs):
      r"""evaluates Venkataraman's sinc function for a list of coeffs
  
      f(x) = -20 * \sin(r(x))/r(x)
  
      Where:
      r(x) = \sqrt((x_0 - 4)^2 + (x_1 - 4)^2 + 0.1)
  
      Inspect with mystic_model_plotter using::
          mystic.models.venkat91 -b "-10:10:.1, -10:10:.1" -d
  
      The minimum is f(x)=-19.668329370585823 at x=(4.0, 4.0)"""
      x, y = coeffs
      R = ((x - 4.0) ** 2 + (y - 4.0) ** 2 + 0.1) ** 0.5
      return -20.0 * sin(R) / R
  
imports: from .abstract_model import AbstractFunction
  from math import sin
label_desc: Use image node_id 2 for calling the Sinc obj's underlying member method code with example usage: obj.function(coeffs) and returns: unknown