Tutorial: Creating the Python Solver file

The porpouse of this file is to act as an interface between your problem's script (also in python) file and the Kratos functions. We will create a class and functions already customized for our type of problem, so that the calls required in the .py from the problem become simpler. The file can be in the /python_scripts folder.

pure_diffusion_solver.py

from __future__ import print_function, absolute_import, division #makes KratosMultiphysics backward compatible with python 2.6 and 2.7
# importing the Kratos Library
import KratosMultiphysics 
import KratosMultiphysics.MyLaplacianApplication as Poisson

# Check that KratosMultiphysics was imported in the main script
KratosMultiphysics.CheckForPreviousImport()

def CreateSolver(model_part, custom_settings):
    return PureDiffusionSolver(model_part, custom_settings)

class PureDiffusionSolver(object):
    def __init__(self, model_part, custom_settings):  # Constructor of the class
        self.model_part  = model_part
        self.domain_size = self.model_part.ProcessInfo[KratosMultiphysics.DOMAIN_SIZE]

        ## Settings string in json format
        default_settings = KratosMultiphysics.Parameters("""
        {
            "model_import_settings"        : {
                "input_type"          : "mdpa",
                "input_filename"      : "unknown_name"
            },
            "echo_level"                   : 0,
            "buffer_size"                  : 2,
            "relative_tolerance"           : 1e-6,
            "absolute_tolerance"           : 1e-9,
            "maximum_iterations"           : 20,
            "compute_reactions"            : false,
            "reform_dofs_at_each_step"     : false,
            "calculate_norm_dx"            : true,
            "move_mesh_flag"               : false,
            "linear_solver_settings"       : {
                    "solver_type"     : "SkylineLUFactorizationSolver"
            }
        }""")

        """
        ## Overwrite the default settings with user-provided parameters
        self.settings = custom_settings
        self.settings.ValidateAndAssignDefaults(default_settings)

        ## Construct the linear solver
        import linear_solver_factory
        self.linear_solver = linear_solver_factory.ConstructSolver(self.settings["linear_solver_settings"])
        """

        # Assign default parameters ADDED
        self.settings = default_settings

        ## Construct the linear solver
        import linear_solver_factory
        self.linear_solver = linear_solver_factory.ConstructSolver(self.settings["linear_solver_settings"])



    def AddVariables(self):
        self.model_part.AddNodalSolutionStepVariable(KratosMultiphysics.TEMPERATURE);
        self.model_part.AddNodalSolutionStepVariable(Poisson.POINT_HEAT_SOURCE);

    def AddDofs(self):
        for node in self.model_part.Nodes:
            node.AddDof(KratosMultiphysics.TEMPERATURE);
        
        print ("variables for the Poisson solver added correctly")

    def GetMinimumBufferSize(self):
        return 1

    def ImportModelPart(self):
        ## Model part reading
        if(self.settings["model_import_settings"]["input_type"].GetString() == "mdpa"):
            ## Here it would be the place to import restart data if required
            KratosMultiphysics.ModelPartIO(self.settings["model_import_settings"]["input_filename"].GetString()).ReadModelPart(self.model_part)
        else:
            raise Exception("Other input options are not yet implemented")
        ## Set the buffer size
        self.model_part.SetBufferSize( self.settings["buffer_size"].GetInt() )
        if(self.GetMinimumBufferSize() > self.model_part.GetBufferSize() ):
            self.model_part.SetBufferSize(self.GetMinimumBufferSize())

    def Initialize(self):

        # Creating the solution strategy
        self.conv_criteria = KratosMultiphysics.DisplacementCriteria(self.settings["relative_tolerance"].GetDouble(),
                                                                     self.settings["absolute_tolerance"].GetDouble())
        (self.conv_criteria).SetEchoLevel(self.settings["echo_level"].GetInt())

        self.time_scheme = KratosMultiphysics.ResidualBasedIncrementalUpdateStaticScheme()

        builder_and_solver = KratosMultiphysics.ResidualBasedBlockBuilderAndSolver(self.linear_solver)

        self.solver = KratosMultiphysics.ResidualBasedLinearStrategy(self.model_part,
                                                                     self.time_scheme,
                                                                     self.linear_solver,
                                                                     self.settings["compute_reactions"].GetBool(),
                                                                     self.settings["reform_dofs_at_each_step"].GetBool(),
                                                                     self.settings["calculate_norm_dx"].GetBool(),
                                                                     self.settings["move_mesh_flag"].GetBool())


        (self.solver).SetEchoLevel(self.settings["echo_level"].GetInt())
        (self.solver).Check()

        (self.solver).Initialize()

        print ("Pure diffusion solver initialization finished")

    def Solve(self):
        # Solve equations on mesh
        (self.solver).Solve()