Introduction
Expressions can be written to the Vtu format and can be easily visualized using any compatible software such as Paraview.
This output is compatible with shared memory and distributed memory parallelization. In shared memory parallelization, it will write only one file having the extension *.vtu. In distributed memory parallelization, it will write one *.vtu file per rank, and then one *.pvtu for all ranks linking all the *.vtu files from all ranks.
Use case
import numpy
# create the numpy expression. This does not need Kratos as long as you know correctly
# the number of local entities (i.e. nodes/conditions/elements) in the model part.
# it is a good practice to specify the "dtype" in here.
# here also, first dimension represent the number of local entities, rest of the
# dimensions represent the dimensionality of the entity data.
numpy_array = numpy.array([
[1,2,3],
[3,4,5]], dtype=numpy.float64)
import KratosMultiphysics as Kratos
model = Kratos.Model()
model_part = model.CreateModelPart("test")
node_1 = model_part.CreateNewNode(1, 0.0, 0.0, 0.0)
node_2 = model_part.CreateNewNode(2, 0.0, 1.0, 0.0)
# now create the expression:
nodal_expression = Kratos.Expression.NodalExpression(model_part)
# now move in the data from numpy array to expression (linking nodal expression with numpy array)
Kratos.Expression.CArrayExpressionIO.Read(nodal_expression, numpy_array)
# creates the vtu output. Needs to be same as the model part used to create the expression
vtu_output = Kratos.VtuOutput(model_part)
# add the expression. First argument is the name to be used in the visualization. second argument is the expression
vtu_output.AddContainerExpression("numpy_array", nodal_expression)
# print the output. Argument specifies the file name prefix.
# this will only print the nodes, since the expression is a nodal expression without any elements.
# if the model part has elements or conditions, then it will print the corresponding geometries with nodal values given in expression.
vtu_output.PrintOutput("output")