Create Custom Items

Items are supported to be used in a Step and in newtonrhapson(). They provide methods to assemble a vector and a sparse matrix. An item has to be created as a class which takes a FieldContainer as input argument. In its __init__(self, field) method, the helpers Assemble and Results have to be evaluated and added as attributes. Internal methods which assemble the sparse vector and matrix, optionally with an updated FieldContainer provided by the field argument, have to be linked to Assemble.

Note

This is only a minimal working example for an item. For more details, see the sources of SolidBody or SolidBodyNearlyIncompressible.

from scipy.sparse import csr_matrix
import felupe as fem


class MyItem:
    def __init__(self, field):
        self.field = field
        self.assemble = fem.mechanics.Assemble(vector=self._vector, matrix=self._matrix)
        self.results = fem.mechanics.Results()

    def _vector(self, field=None, **kwargs):
        return csr_matrix(([0.0], ([0], [0])), shape=(1, 1))

    def _matrix(self, field=None, **kwargs):
        return csr_matrix(([0.0], ([0], [0])), shape=(1, 1))

This item is now added to a basic script.

Note

The vector- and matrix-shapes are automatically increased to match the shape of the other items if necessary. Hence, a sparse matrix with shape (1, 1) is a valid choice for a vector or a matrix filled with zeros.

region = fem.RegionHexahedron(mesh=fem.Cube(n=3))
field = fem.FieldContainer([fem.Field(region, dim=3)])
boundaries, loadcase = fem.dof.uniaxial(field, clamped=True, move=1.0)

solid = fem.SolidBody(umat=fem.NeoHooke(mu=1, bulk=2), field=field)
my_item = MyItem(field=field)

step = fem.Step(items=[solid, my_item], boundaries=boundaries)
job = fem.Job(steps=[step]).evaluate()