TreeQAOA

TreeQAOA#

class iqm.qaoa.tree_qaoa.TreeQAOA(problem, num_layers, *, betas=None, gammas=None, initial_angles=None)[source]#

Bases: QUBOQAOA

The class for tree QAOA with QUBO cost function.

The class inherits everything from QUBOQAOA, but adds one more method set_tree_angles(), which sets angles according to the tree schedule. The tree schedule uses QAOA angles precalculated numerically for a class of high-girth regular graph problems with uniform Hamiltonian. For more details see [7].

Parameters:

  • problem (QUBOInstance | ConstrainedQuadraticInstance) – A QUBOInstance object describing the QUBO problem to be solved.

  • num_layers (int) – The number of QAOA layers, commonly referred to as p in the literature.

  • betas (Sequence[float] | ndarray | None) – An optional list of the initial beta angles of QAOA. Has to be provided together with gammas.

  • gammas (Sequence[float] | ndarray | None) – An optional list of the initial gamma angles of QAOA. Has to be provided together with betas.

  • initial_angles (Sequence[float] | ndarray | None) – An optional list of the initial QAOA angles as one variable. Shouldn’t be provided together with either betas or gammas.

Attributes

Methods

set_tree_angles()

A method for setting iqm.qaoa.generic_qaoa.QAOA.angles according to the tree schedule.
set_tree_angles()[source]#

A method for setting iqm.qaoa.generic_qaoa.QAOA.angles according to the tree schedule.

The tree schedule is designed for problems with uniform 1-body local field, unit 2-body interactions and uniform node degree. Therefore, when given a generic problem, the algorithm first calculates the average degree d_av, the average local field h_av and the average interaction strength j_av (which is used to renormalize the local field). The angles are then looked up in the saved files for the nearest implemented degree and local field. For \(p > 6\) QAOA, the angles are interpolated from the calculated angles for \(p = 6\). The method doesn’t output anything, but it modifies iqm.qaoa.generic_qaoa.QAOA.angles in-place.

Raises:

ValueError – If the Hamiltonian contains ferromagnetic (i.e., negative) interactions between qubits. The tree schedule shouldn’t be used for such cases.

Return type:

None