decogo.pyomo_input_model.input_model

This modules construct user-defined Pyomo minlp input model for refactory CG algorithm.

Classes

PyomoInputModel(model)	This class implement user-defined input model for Pyomo MINLP problems.
PyomoOriginalProblem(sub_models, cuts, settings)	This class implement user-defined primal heuristis for pyomo MINLP problems.
PyomoSubModel(model, vars_in_block, block_id)	Container class which stores the variables from the single block and local nonlinear constraints.
PyomoSubProblems(sub_models, cuts, block_id, ...)	Container class for managing all sub-problems

class decogo.pyomo_input_model.input_model.PyomoInputModel(model)

This class implement user-defined input model for Pyomo MINLP problems.

Parameters

• model (ConcreteModel) – Input Pyomo model

• blocks (list) – List (blockwise) of original string names of variables

• block_sizes (list) – List of variable numbers per sub-model

• sense (int) – Indicates the the problem is minimization (1) or maximization (-1)

• sub_problems (list) – list of SubProblems blockwise

• original_problem (PyomoOriginalProblem) – container of original problem

• cuts (decogo.model.constraints.CutPool) – container of linear constraints

• sub_models (list) – list of containers for variables from a single block and local nonlinear constraints blockwise

__init__(model)

_construct_cut_pool()

An abstract method for generating the parameters of cut_pool

Returns

block_sizes, blocks, obj, global_cuts, local_cuts

Return type

tuple

_read_constraint_object(con_obj, local_cuts, global_cuts)

Reads Pyomo constraints, detects if the constraint is linear. If yes, then it creates the linear constraint

Parameters

con_obj (Constraint) – Pyomo constraint object

_get_linear_term_data(expr)

Recursive function for reading and getting data for linear terms

Parameters

expr (Expression) – Linear expression to parse

Returns

List of coefficients and constant

Return type

(list, int)

_get_variable_index_by_name(var_name)

Get variable index from the list of blocks for sparse vector initialization

Parameters

var_name (str) – Original variable name

Returns

Pair of indices: block id and index in the block

Return type

(int, int)

static _remove_unpicklable_objects_pyomo_model(model)

Removes unpicklable objects from Pyomo model object. This is because multiprocessing is based on serialization and some objects cannot be serialized (pickled). This method does the following:

• removes objects Port and Arcs, since they contain weakref objects

• sets to None the ‘rule’ property for Constraint, Objective and Param, since it might contain lambda function

• sets to None property ‘initialize’ and ‘_init_values._init’ for Set, since it might contain lambda function

Parameters

model (ConcreteModel) – Pyomo model

__abstractmethods__ = frozenset({})

_abc_impl = <_abc_data object>

class decogo.pyomo_input_model.input_model.PyomoOriginalProblem(sub_models, cuts, settings)

This class implement user-defined primal heuristis for pyomo MINLP problems.

Parameters

• cuts (CutPool) – Container which stores all linear constraints (global and local) and objective function

• sub_models (list) – List of sub-models

• nlp_problem (NlpProblem) – NLP master problem

• mip_projection_master_problem – MIP projection master problem

• nlp_resource_projection_problem (NlpResourceProjectionProblem) – NLP projection master problem

__init__(sub_models, cuts, settings)

Constructor method

local_solve_fast(start_point, result, problem, iter=None)

Abstract method for fast solving original problem non-optimal/heuristically/locally

Parameters

• start_point (ndarray) – Starting point for the solver, defaults to None

• result (Results) – stores and makes some manipulations with the CG results

• problem (DecomposedProblem) – stores all problem objects

• iter (int) – index of iterations in main algorithm

local_solve(start_point, result, problem, iter=None)

Abstract method for solving original problem non-optimal/heuristically/locally

Parameters

• start_point (ndarray) – Starting point for the solver, defaults to None

• result (Results) – stores and makes some manipulations with the CG results

• problem (DecomposedProblem) – stores all problem objects

• iter (int) – index of iterations in main algorithm

nlp_solve(solver_name, point_to_fix=None, start_point=None, cut_direction=None)

Solves NlpProblem. Solved mostly with fixed integer variables

Parameters

• solver_name (str) – External solver name

• point_to_fix (BlockVector) – Point to be fixed using the integer variables

• start_point (BlockVector) – Point for the warm start for the external solver

• cut_direction (BlockVector) – Objective direction

Returns

Solution point, objective value, flag if the solution point is feasible

Return type

tuple

solve_mip_proj_problem(solver_name, point_to_project, target_value=inf, pool_solutions=100)

Solves MipProjectionMasterProblem

Parameters

• solver_name (str) – External solver name

• point_to_project (BlockVector) – Point to project from, it is in the original space

Returns

Solution point, objective value

Return type

tuple

solve_nlp_resource_proj_problem(solver_name, point_to_project, target_value=inf, start_point=None)

Solves NlpResourceProjectionProblem

Parameters

• solver_name (str) – External solver name

• point_to_project (BlockVector) – Point to project from, it is in the image space

• start_point (BlockVector) – Starting point for external solver

Returns

Solution point, objective value, flag indicating if the solution point is infeasible, slack value of the soft fixing of target cut

Return type

tuple

__abstractmethods__ = frozenset({})

_abc_impl = <_abc_data object>

class decogo.pyomo_input_model.input_model.PyomoSubModel(model, vars_in_block, block_id)

Container class which stores the variables from the single block and local nonlinear constraints.

Parameters

• model (ConcreteModel) – Input Pyomo model

• vars_in_block (list) – List of original variable names from the model

• block_id (int) – Identifier for block

• variables (list) – List of all variables with all necessary properties

• block_size (int) – Number of variables in the sub-model

• integer (bool) – Indicates if the current sub-model contains variable of integer type

• nonlin_constr (list) – List of local nonlinear constraints stored using original Pyomo expression

__init__(model, vars_in_block, block_id)

Constructor method

read_nonlinear_constraint(con_obj)

Determines if the given constraint belongs to this sub-model. If yes, it adds to the list of nonlinear constraints by copying the Pyomo expression

Parameters

con_obj (ScalarConstraint or IndexedConstraint) – Pyomo constraint object

constraint_vars_in_block(expr)

Checks if the Pyomo expression belongs to the current sub-model

Parameters

expr (Expression) – Pyomo expression.

compute_gradients()

Computes gradients for each nonlinear constraint and stores in the constraint object

round(point)

Round point to the closest integer

Parameters

point (ndarray) – Given point

Returns

New rounded point

Return type

ndarray

__abstractmethods__ = frozenset({})

_abc_impl = <_abc_data object>

class decogo.pyomo_input_model.input_model.PyomoSubProblems(sub_models, cuts, block_id, settings)

Container class for managing all sub-problems

Parameters

• minlp_sub_problem (PyomoMinlpSubProblem) – Sub-probem with linear objective

• proj_sub_problem (PyomoProjectionSubProblem) – Pure projection sub-problem

• resource_constrained_sub_problem (PyomoResourceConstrainedSubProblem) – Resource constrained sub-problem for checking the feasibility of the resources

• line_search_sub_problem (PyomoLineSearchSubProblem) – Line search sub-problem

__init__(sub_models, cuts, block_id, settings)

Constructor method :param approx_data:

global_solve(result, direction, start_point=None)

An abstract method for solving sub-problem globally/near-optimal or calling an exact solver

Parameters

• result (Results) – stores and makes some manipulations with the CG results

• direction (ndarray) – Given vector

• start_point (ndaray or None) – Starting point for the solver, defaults to None

Returns

Solution point (ndarray), primal bound, dual bound, flag if the primal bound is feasible

Return type

tuple

local_solve(result, direction, start_point=None)

An abstract method for solving sub-problem non-optimal/heuristically/locally

Parameters

• result (Results) – stores and makes some manipulations with the CG results

• direction (ndarray) – Given vector

• start_point (ndarray or None) – Starting point for the solver, defaults to None

Returns

Solution point (ndarray), primal bound, dual bound, flag if the primal bound is feasible

Return type

tuple

minlp_solve(solver_name, solver_options=None, start_point=None, direction=None, cell=None)

Solves MinlpSubProblem

Parameters

• solver_name (str) – External solver name

• solver_options (list or None) – External solver options, defaults to None

• start_point (ndarray or None) – Staring point for the solver, defaults to None

• direction (ndarray or None) – Direction for the objective, defaults to None

• cell (Cell or None) – Cell, defaults to None

Returns

Solution point, primal and dual bound

Return type

tuple

fixed_minlp_solve(solver_name, start_point, solver_options=None, direction=None, cell=None)

Solves MinlpSubProblem with fixed integer variables

Parameters

• solver_name (str) – External solver name

• start_point (ndarray or None) – Staring point for the solver, and point which is used for fixing the integers

• solver_options (list or None) – External solver options, defaults to None

• direction (ndarray or None) – Direction for the objective, defaults to None

• cell (Cell or None) – Cell, defaults to None

Returns

Solution point, primal and dual bound

Return type

tuple

nlp_proj_solve(solver_name, point_to_project, start_point=None)

Solves ProjSubProblem

Parameters

• solver_name (str) – External solver name

• point_to_project (ndarray) – Projection point

• start_point (ndarray or None) – Staring point for the solver, defaults to None

Returns

Solution point, primal bound and flag indicating the feasibility of primal solution

Return type

tuple

resource_proj_solve(solver_name, point_to_project, solver_options=None, start_point=None)

Solves ResourceProjSubProblem

Parameters

• solver_name (str) – External solver name

• point_to_project (ndarray) – Projection point

• start_point (ndarray or None) – Staring point for the solver, defaults to None

Returns

Solution point, primal bound and flag indicating the feasibility of primal solution

Return type

tuple

solve_line_search_subproblem(solver_name, exterior_point, interior_point)

Solves LineSearchSubProblem

Parameters

• solver_name (str) – External solver name

• exterior_point (ndarray) – Exterior point

• interior_point (ndarray) – Interior point

Returns

value of parameter \(\alpha\) and solution point

Return type

tuple

add_linear_constraint()

Adds linear constraints to sub-problems

update_var_lower_bound(index)

Updates the lower bound of variable by index

Parameters

index (tuple) – Index of the variable (block_id, index)

update_var_upper_bound(index)

Updates the upper bound of variable by index

Parameters

index (tuple) – Index of the variable (block_id, index)

__abstractmethods__ = frozenset({})

_abc_impl = <_abc_data object>