CobylaOptimizer
class CobylaOptimizer(rhobeg=1.0, rhoend=0.0001, maxfun=1000, disp=None, catol=0.0002, trials=1, clip=100.0)
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
>>> problem = QuadraticProgram()
>>> # 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-cliporclipvalues correspondingly for the initial guesses.
Methods
get_compatibility_msg
CobylaOptimizer.get_compatibility_msg(problem)
Checks whether a given problem can be solved with this optimizer.
Checks whether the given problem is compatible, i.e., whether the problem contains only continuous variables, and otherwise, returns a message explaining the incompatibility.
Parameters
problem (QuadraticProgram) – The optimization problem to check compatibility.
Return type
str
Returns
Returns a string describing the incompatibility.
is_compatible
CobylaOptimizer.is_compatible(problem)
Checks whether a given problem can be solved with the optimizer implementing this method.
Parameters
problem (QuadraticProgram) – The optimization problem to check compatibility.
Return type
bool
Returns
Returns True if the problem is compatible, False otherwise.
multi_start_solve
CobylaOptimizer.multi_start_solve(minimize, problem)
Applies a multi start method given a local optimizer.
Parameters
- minimize (
Callable[[ndarray],Tuple[ndarray,Any]]) – A callable object that minimizes the problem specified - problem (
QuadraticProgram) – A problem to solve
Return type
OptimizationResult
Returns
The result of the multi start algorithm applied to the problem.
solve
CobylaOptimizer.solve(problem)
Tries to solves the given problem using the optimizer.
Runs the optimizer to try to solve the optimization problem.
Parameters
problem (QuadraticProgram) – The problem to be solved.
Return type
OptimizationResult
Returns
The result of the optimizer applied to the problem.
Raises
QiskitOptimizationError – If the problem is incompatible with 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.