class_docstr: Test the Rotoselect (gradient-free) optimizer
class_docstr_tok: ["Test","the","Rotoselect","(","gradient-free",")","optimizer"]
docstr: Helper function to test the Rotosolve and Rotoselect optimizers
docstr_tok: ["Helper","function","to","test","the","Rotosolve","and","Rotoselect","optimizers"]
code: def rotosolve_step(f, x):
      """Helper function to test the Rotosolve and Rotoselect optimizers"""
      # make sure that x is an array
      if np.ndim(x) == 0:
          x = np.array([x])
  
      # helper function for x[d] = theta
      def insert(xf, d, theta):
          xf[d] = theta
          return xf
  
      for d, _ in enumerate(x):
          H_0 = float(f(insert(x, d, 0)))
          H_p = float(f(insert(x, d, np.pi / 2)))
          H_m = float(f(insert(x, d, -np.pi / 2)))
          a = onp.arctan2(2 * H_0 - H_p - H_m, H_p - H_m)
  
          x[d] = -np.pi / 2 - a
  
          if x[d] <= -np.pi:
              x[d] += 2 * np.pi
      return x
  
file_path: pennylane/tests/optimize/test_rotoselect.py
imports: import itertools
  import numpy
  import pytest
  import pennylane
  from pennylane import numpy
  from pennylane.optimize import RotoselectOptimizer
label_desc: Use image node_id 5 for calling the TestRotoselectOptimizer obj's underlying member method code with example usage: obj.rotosolve_step(f, x) and returns: x, xf