# differential_evolution_driver.py¶

Driver for a differential evolution genetic algorithm.

TODO: add better references than: https://en.wikipedia.org/wiki/Differential_evolution

Most of this driver (except execute_ga) is based on SimpleGA, so the following may still apply:

The following reference is only for the penalty function: Smith, A. E., Coit, D. W. (1995) Penalty functions. In: Handbook of Evolutionary Computation, 97(1).

The following reference is only for weighted sum multi-objective optimization: Sobieszczanski-Sobieski, J., Morris, A. J., van Tooren, M. J. L. (2015) Multidisciplinary Design Optimization Supported by Knowledge Based Engineering. John Wiley & Sons, Ltd.

class`openmdao.drivers.differential_evolution_driver.`

`DifferentialEvolution`

(objfun,comm=None,model_mpi=None)[source]Bases:

`object`

Differential Evolution Genetic Algorithm.

TODO : add better references than: https://en.wikipedia.org/wiki/Differential_evolution

- Attributes

commMPI communicator or NoneThe MPI communicator that will be used objective evaluation for each generation.

lchromintChromosome length.

model_mpiNone or tupleIf the model in objfun is also parallel, then this will contain a tuple with the the total number of population points to evaluate concurrently, and the color of the point to evaluate on this rank.

npopintPopulation size.

objfunfunctionObjective function callback.

`__init__`

(objfun,comm=None,model_mpi=None)[source]Initialize genetic algorithm object.

- Parameters

objfunfunctionObjective callback function.

commMPI communicator or NoneThe MPI communicator that will be used objective evaluation for each generation.

model_mpiNone or tupleIf the model in objfun is also parallel, then this will contain a tuple with the the total number of population points to evaluate concurrently, and the color of the point to evaluate on this rank.

`execute_ga`

(x0,vlb,vub,pop_size,max_gen,random_state,F=0.5,Pc=0.5)[source]Perform the genetic algorithm.

- Parameters

x0ndarrayInitial design values

vlbndarrayLower bounds array.

vubndarrayUpper bounds array.

pop_sizeintNumber of points in the population.

max_genintNumber of generations to run the GA.

random_statenp.random.RandomState, intRandom state (or seed-number) which controls the seed and random draws.

FfloatDifferential rate

PcfloatCrossover rate

- Returns

- ndarray
Best design point

- float
Objective value at best design point.

- int
Number of successful function evaluations.

class`openmdao.drivers.differential_evolution_driver.`

`DifferentialEvolutionDriver`

(**kwargs)[source]Bases:

`openmdao.core.driver.Driver`

Driver for a differential evolution genetic algorithm.

This algorithm requires that inputs are floating point numbers.

- Attributes

_concurrent_pop_sizeintNumber of points to run concurrently when model is a parallel one.

_concurrent_colorintColor of current rank when running a parallel model.

_desvar_idxdictKeeps track of the indices for each desvar, since DifferentialEvolution sees an array of design variables.

_ga<DifferentialEvolution>Main genetic algorithm lies here.

_randomstatenp.random.RandomState, intRandom state (or seed-number) which controls the seed and random draws.

`__init__`

(**kwargs)[source]Initialize the DifferentialEvolutionDriver driver.

- Parameters

**kwargsdict of keyword argumentsKeyword arguments that will be mapped into the Driver options.

`add_recorder`

(recorder)Add a recorder to the driver.

- Parameters

recorderCaseRecorderA recorder instance.

`cleanup`

()Clean up resources prior to exit.

`declare_coloring`

(num_full_jacs=3,tol=1e-25,orders=None,perturb_size=1e-09,min_improve_pct=5.0,show_summary=True,show_sparsity=False)Set options for total deriv coloring.

- Parameters

num_full_jacsintNumber of times to repeat partial jacobian computation when computing sparsity.

tolfloatTolerance used to determine if an array entry is nonzero during sparsity determination.

ordersintNumber of orders above and below the tolerance to check during the tolerance sweep.

perturb_sizefloatSize of input/output perturbation during generation of sparsity.

min_improve_pctfloatIf coloring does not improve (decrease) the number of solves more than the given percentage, coloring will not be used.

show_summaryboolIf True, display summary information after generating coloring.

show_sparsityboolIf True, display sparsity with coloring info after generating coloring.

`get_constraint_values`

(ctype='all',lintype='all',driver_scaling=True)Return constraint values.

- Parameters

ctypestringDefault is ‘all’. Optionally return just the inequality constraints with ‘ineq’ or the equality constraints with ‘eq’.

lintypestringDefault is ‘all’. Optionally return just the linear constraints with ‘linear’ or the nonlinear constraints with ‘nonlinear’.

driver_scalingboolWhen True, return values that are scaled according to either the adder and scaler or the ref and ref0 values that were specified when add_design_var, add_objective, and add_constraint were called on the model. Default is True.

- Returns

- dict
Dictionary containing values of each constraint.

`get_design_var_values`

(get_remote=True,driver_scaling=True)Return the design variable values.

- Parameters

get_remotebool or NoneIf True, retrieve the value even if it is on a remote process. Note that if the variable is remote on ANY process, this function must be called on EVERY process in the Problem’s MPI communicator. If False, only retrieve the value if it is on the current process, or only the part of the value that’s on the current process for a distributed variable.

driver_scalingboolWhen True, return values that are scaled according to either the adder and scaler or the ref and ref0 values that were specified when add_design_var, add_objective, and add_constraint were called on the model. Default is True.

- Returns

- dict
Dictionary containing values of each design variable.

`get_objective_values`

(driver_scaling=True)Return objective values.

- Parameters

driver_scalingboolWhen True, return values that are scaled according to either the adder and scaler or the ref and ref0 values that were specified when add_design_var, add_objective, and add_constraint were called on the model. Default is True.

- Returns

- dict
Dictionary containing values of each objective.

property`msginfo`

Return info to prepend to messages.

- Returns

- str
Info to prepend to messages.

`objective_callback`

(x,icase)[source]Evaluate problem objective at the requested point.

In case of multi-objective optimization, a simple weighted sum method is used:

\[f = (\sum_{k=1}^{N_f} w_k \cdot f_k)^a\]where \(N_f\) is the number of objectives and \(a>0\) is an exponential weight. Choosing \(a=1\) is equivalent to the conventional weighted sum method.

The weights given in the options are normalized, so:

\[\sum_{k=1}^{N_f} w_k = 1\]If one of the objectives \(f_k\) is not a scalar, its elements will have the same weights, and it will be normed with length of the vector.

Takes into account constraints with a penalty function.

All constraints are converted to the form of \(g_i(x) \leq 0\) for inequality constraints and \(h_i(x) = 0\) for equality constraints. The constraint vector for inequality constraints is the following:

\[ \begin{align}\begin{aligned}g = [g_1, g_2 \dots g_N], g_i \in R^{N_{g_i}}\\h = [h_1, h_2 \dots h_N], h_i \in R^{N_{h_i}}\end{aligned}\end{align} \]The number of all constraints:

\[N_g = \sum_{i=1}^N N_{g_i}, N_h = \sum_{i=1}^N N_{h_i}\]The fitness function is constructed with the penalty parameter \(p\) and the exponent \(\kappa\):

\[\Phi(x) = f(x) + p \cdot \sum_{k=1}^{N^g}(\delta_k \cdot g_k)^{\kappa} + p \cdot \sum_{k=1}^{N^h}|h_k|^{\kappa}\]where \(\delta_k = 0\) if \(g_k\) is satisfied, 1 otherwise

Note

The values of \(\kappa\) and \(p\) can be defined as driver options.

- Parameters

xndarrayValue of design variables.

icaseintCase number, used for identification when run in parallel.

- Returns

- float
Objective value

- bool
Success flag, True if successful

- int
Case number, used for identification when run in parallel.

`record_iteration`

()Record an iteration of the current Driver.

`run`

()[source]Execute the genetic algorithm.

- Returns

- boolean
Failure flag; True if failed to converge, False is successful.

`scaling_report`

(outfile='driver_scaling_report.html',title=None,show_browser=True,jac=True)Generate a self-contained html file containing a detailed connection viewer.

Optionally pops up a web browser to view the file.

- Parameters

outfilestr, optionalThe name of the output html file. Defaults to ‘driver_scaling_report.html’.

titlestr, optionalSets the title of the web page.

show_browserbool, optionalIf True, pop up a browser to view the generated html file. Defaults to True.

jacboolIf True, show jacobian information.

- Returns

- dict
Data used to create html file.

`set_design_var`

(name,value,set_remote=True)Set the value of a design variable.

- Parameters

namestrGlobal pathname of the design variable.

valuefloat or ndarrayValue for the design variable.

set_remoteboolIf True, set the global value of the variable (value must be of the global size). If False, set the local value of the variable (value must be of the local size).

`use_fixed_coloring`

(coloring=<object object>)Tell the driver to use a precomputed coloring.

- Parameters

coloringstrA coloring filename. If no arg is passed, filename will be determined automatically.