class_docstr: Matyas objective function.
  
  This class defines the Matyas [1]_ global optimization problem. This is a
  multimodal minimization problem defined as follows:
  
  .. math::
  
      f_{\text{Matyas}}(x) = 0.26(x_1^2 + x_2^2) - 0.48 x_1 x_2
  
  
  with :math:`x_i \in [-10, 10]` for :math:`i = 1, 2`.
  
  *Global optimum*: :math:`f(x) = 0` for :math:`x = [0, 0]`
  
  .. [1] Jamil, M. & Yang, X.-S. A Literature Survey of Benchmark Functions
  For Global Optimization Problems Int. Journal of Mathematical Modelling
  and Numerical Optimisation, 2013, 4, 150-194.
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code: def fun(self, x, *args):
      self.nfev += 1
  
      return 0.26 * (x[0] ** 2 + x[1] ** 2) - 0.48 * x[0] * x[1]
  
imports: from numpy import abs, asarray, cos, exp, log, arange, pi, prod, sin, sqrt, sum, tan
  from .go_benchmark import Benchmark, safe_import
label_desc: Use image node_id 2 for calling the Matyas obj's underlying member method code with example usage: obj.fun(x) and returns: unknown