# CobylaOptimizer¶

class CobylaOptimizer(rhobeg=1.0, rhoend=0.0001, maxfun=1000, disp=None, catol=0.0002, trials=1, clip=100.0)[source]

Bases: qiskit.optimization.algorithms.multistart_optimizer.MultiStartOptimizer

The SciPy COBYLA optimizer wrapped as an Qiskit OptimizationAlgorithm.

This class provides a wrapper for scipy.optimize.fmin_cobyla (https://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.optimize.fmin_cobyla.html) to be used within the optimization module. The arguments for fmin_cobyla are passed via the constructor.

Examples

>>> from qiskit.optimization.problems import QuadraticProgram
>>> from qiskit.optimization.algorithms import CobylaOptimizer
>>> # specify problem here
>>> optimizer = CobylaOptimizer()
>>> result = optimizer.solve(problem)


Initializes the CobylaOptimizer.

This initializer takes the algorithmic parameters of COBYLA and stores them for later use of fmin_cobyla when solve() is invoked. This optimizer can be applied to find a (local) optimum for problems consisting of only continuous variables.

Parameters
• rhobeg (float) – Reasonable initial changes to the variables.

• rhoend (float) – Final accuracy in the optimization (not precisely guaranteed). This is a lower bound on the size of the trust region.

• disp (Optional[int]) – Controls the frequency of output; 0 implies no output. Feasible values are {0, 1, 2, 3}.

• maxfun (int) – Maximum number of function evaluations.

• catol (float) – Absolute tolerance for constraint violations.

• trials (int) – The number of trials for multi-start method. The first trial is solved with the initial guess of zero. If more than one trial is specified then initial guesses are uniformly drawn from [lowerbound, upperbound] with potential clipping.

• clip (float) – Clipping parameter for the initial guesses in the multi-start method. If a variable is unbounded then the lower bound and/or upper bound are replaced with the -clip or clip values correspondingly for the initial guesses.

Methods

 get_compatibility_msg Checks whether a given problem can be solved with this optimizer. is_compatible Checks whether a given problem can be solved with the optimizer implementing this method. multi_start_solve Applies a multi start method given a local optimizer. solve Tries to solves the given problem using the optimizer.

Attributes

clip

Returns the clip value for this optimizer.

Return type

float

Returns

The clip value.

trials

Returns the number of trials for this optimizer.

Return type

int

Returns

The number of trials.