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I want to find the estimate of the ground state energy of my Hamiltonian H that is implemented as PauliSumOp in my variable H_op. I then prepare an ansatz circuit circ_ansatz with 5 parameters. Then I try to run the thing with my_vqe = VQE(ansatz = circ_ansatz, optimizer=SPSA, quantum_instance=Aer.get_backend('aer_simulator'), initial_point=[0.5]*N_iters) and then print(my_vqe.compute_minimum_eigenvalue(H_op)) but I get the following error: print(my_vqe.compute_minimum_eigenvalue(H_op)) File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/qiskit/algorithms/minimum_eigen_solvers/vqe.py", line 526, in compute_minimum_eigenvalue opt_result = self.optimizer( # pylint: disable=not-callable TypeError: __init__() got an unexpected keyword argument 'fun'

Any help is highly appreciated!

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my_vqe = VQE(ansatz = circ_ansatz, optimizer=SPSA,...

You need to make an instance of the optimizer not pass the class (set any parameters you want the following uses defaults)

my_vqe = VQE(ansatz = circ_ansatz, optimizer=SPSA(),...

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