UMDA¶
- class UMDA(maxiter=100, size_gen=20, alpha=0.5)[código fonte]¶
Bases:
Optimizer
Continuous Univariate Marginal Distribution Algorithm (UMDA).
UMDA [1] is a specific type of Estimation of Distribution Algorithm (EDA) where new individuals are sampled from univariate normal distributions and are updated in each iteration of the algorithm by the best individuals found in the previous iteration.
Veja também
This original implementation of the UDMA optimizer for Qiskit was inspired by my (Vicente P. Soloviev) work on the EDAspy Python package [2].
EDAs are stochastic search algorithms and belong to the family of the evolutionary algorithms. The main difference is that EDAs have a probabilistic model which is updated in each iteration from the best individuals of previous generations (elite selection). Depending on the complexity of the probabilistic model, EDAs can be classified in different ways. In this case, UMDA is a univariate EDA as the embedded probabilistic model is univariate.
UMDA has been compared to some of the already implemented algorithms in Qiskit library to optimize the parameters of variational algorithms such as QAOA or VQE and competitive results have been obtained [1]. UMDA seems to provide very good solutions for those circuits in which the number of layers is not big.
The optimization process can be personalized depending on the paremeters chosen in the initialization. The main parameter is the population size. The bigger it is, the final result will be better. However, this increases the complexity of the algorithm and the runtime will be much heavier. In the work [1] different experiments have been performed where population size has been set to 20 - 30.
Nota
The UMDA implementation has more parameters but these have default values for the initialization for better understanding of the user. For example,
lpha
parameter has been set to 0.5 and is the percentage of the population which is selected in each iteration to update the probabilistic model.Example
This short example runs UMDA to optimize the parameters of a variational algorithm. Here we will use the same operator as used in the algorithms introduction, which was originally computed by Qiskit Nature for an H2 molecule. The minimum energy of the H2 Hamiltonian can be found quite easily so we are able to set maxiters to a small value.
from qiskit.opflow import X, Z, I from qiskit import Aer from qiskit.algorithms.optimizers import UMDA from qiskit.algorithms import QAOA from qiskit.utils import QuantumInstance H2_op = (-1.052373245772859 * I ^ I) + (0.39793742484318045 * I ^ Z) + (-0.39793742484318045 * Z ^ I) + (-0.01128010425623538 * Z ^ Z) + (0.18093119978423156 * X ^ X) p = 2 # Toy example: 2 layers with 2 parameters in each layer: 4 variables opt = UMDA(maxiter=100, size_gen=20) backend = Aer.get_backend('statevector_simulator') vqe = QAOA(opt, quantum_instance=QuantumInstance(backend=backend), reps=p) result = vqe.compute_minimum_eigenvalue(operator=H2_op)
If it is desired to modify the percentage of individuals considered to update the probabilistic model, then this code can be used. Here for example we set the 60% instead of the 50% predefined.
opt = UMDA(maxiter=100, size_gen=20, alpha = 0.6) backend = Aer.get_backend('statevector_simulator') vqe = QAOA(opt, quantum_instance=QuantumInstance(backend=backend), reps=p) result = vqe.compute_minimum_eigenvalue(operator=qubit_op)
References
[1]: Vicente P. Soloviev, Pedro Larrañaga and Concha Bielza (2022, July). Quantum Parametric Circuit Optimization with Estimation of Distribution Algorithms. In 2022 The Genetic and Evolutionary Computation Conference (GECCO). DOI: https://doi.org/10.1145/3520304.3533963
[2]: Vicente P. Soloviev. Python package EDAspy. https://github.com/VicentePerezSoloviev/EDAspy.
- Parâmetros
maxiter (int) – Maximum number of iterations.
size_gen (int) – Population size of each generation.
alpha (float) – Percentage (0, 1] of the population to be selected as elite selection.
Methods
Get the support level dictionary.
We compute the gradient with the numeric differentiation in the parallel way, around the point x_center.
Minimize the scalar function.
Print algorithm-specific options.
Set max evals grouped
Sets or updates values in the options dictionary.
Wrap the function to implicitly inject the args at the call of the function.
Attributes
- ELITE_FACTOR = 0.4¶
- STD_BOUND = 0.3¶
- alpha¶
Returns the alpha parameter value (percentage of population selected to update probabilistic model)
- bounds_support_level¶
Returns bounds support level
- gradient_support_level¶
Returns gradient support level
- initial_point_support_level¶
Returns initial point support level
- is_bounds_ignored¶
Returns is bounds ignored
- is_bounds_required¶
Returns is bounds required
- is_bounds_supported¶
Returns is bounds supported
- is_gradient_ignored¶
Returns is gradient ignored
- is_gradient_required¶
Returns is gradient required
- is_gradient_supported¶
Returns is gradient supported
- is_initial_point_ignored¶
Returns is initial point ignored
- is_initial_point_required¶
Returns is initial point required
- is_initial_point_supported¶
Returns is initial point supported
- maxiter¶
Returns the maximum number of iterations
- setting¶
Return setting
- settings¶
- size_gen¶
Returns the size of the generations (number of individuals per generation)