"""
Utility functions based on igakit.
"""
from __future__ import absolute_import
import numpy as nm
from sfepy.base.base import Struct
from sfepy.discrete.fem import Mesh
from sfepy.mesh.mesh_generators import get_tensor_product_conn
import six
from six.moves import range
[docs]def create_linear_fe_mesh(nurbs, pars=None):
"""
Convert a NURBS object into a nD-linear tensor product FE mesh.
Parameters
----------
nurbs : igakit.nurbs.NURBS instance
The NURBS object.
pars : sequence of array, optional
The values of parameters in each parametric dimension. If not given,
the values are set so that the resulting mesh has the same number of
vertices as the number of control points/basis functions of the NURBS
object.
Returns
-------
coors : array
The coordinates of mesh vertices.
conn : array
The vertex connectivity array.
desc : str
The cell kind.
"""
knots = nurbs.knots
shape = nurbs.weights.shape
if pars is None:
pars = []
for ii, kv in enumerate(knots):
par = nm.linspace(kv[0], kv[-1], shape[ii])
pars.append(par)
coors = nurbs(*pars)
coors.shape = (-1, coors.shape[-1])
conn, desc = get_tensor_product_conn([len(ii) for ii in pars])
if (coors[:, -1] == 0.0).all():
coors = coors[:, :-1]
return coors, conn, desc
[docs]def create_mesh_and_output(nurbs, pars=None, **kwargs):
"""
Create a nD-linear tensor product FE mesh using
:func:`create_linear_fe_mesh()`, evaluate field variables given as keyword
arguments in the mesh vertices and create a dictionary of output data
usable by Mesh.write().
Parameters
----------
nurbs : igakit.nurbs.NURBS instance
The NURBS object.
pars : sequence of array, optional
The values of parameters in each parametric dimension. If not given,
the values are set so that the resulting mesh has the same number of
vertices as the number of control points/basis functions of the NURBS
object.
**kwargs : kwargs
The field variables as keyword arguments. Their names serve as keys in
the output dictionary.
Returns
-------
mesh : Mesh instance
The finite element mesh.
out : dict
The output dictionary.
"""
coors, conn, desc = create_linear_fe_mesh(nurbs, pars)
mat_id = nm.zeros(conn.shape[0], dtype=nm.int32)
mesh = Mesh.from_data('nurbs', coors, None, [conn], [mat_id], [desc])
out = {}
for key, variable in six.iteritems(kwargs):
if variable.ndim == 2:
nc = variable.shape[1]
field = variable.reshape(nurbs.weights.shape + (nc,))
else:
field = variable.reshape(nurbs.weights.shape)
nc = 1
vals = nurbs.evaluate(field, *pars)
out[key] = Struct(name='output_data', mode='vertex',
data=vals.reshape((-1, nc)))
return mesh, out
[docs]def save_basis(nurbs, pars):
"""
Save a NURBS object basis on a FE mesh corresponding to the given
parametrization in VTK files.
Parameters
----------
nurbs : igakit.nurbs.NURBS instance
The NURBS object.
pars : sequence of array, optional
The values of parameters in each parametric dimension.
"""
coors, conn, desc = create_linear_fe_mesh(nurbs, pars)
mat_id = nm.zeros(conn.shape[0], dtype=nm.int32)
mesh = Mesh.from_data('nurbs', coors, None, [conn], [mat_id], [desc])
n_dof = nurbs.weights.ravel().shape[0]
variable = nm.zeros(n_dof, dtype=nm.float64)
field = variable.reshape(nurbs.weights.shape)
for ic in range(n_dof):
variable[ic - 1] = 0.0
variable[ic] = 1.0
vals = nurbs.evaluate(field, *pars).reshape((-1))
out = {}
out['bf'] = Struct(name='output_data', mode='vertex',
data=vals[:, None])
mesh.write('iga_basis_%03d.vtk' % ic, io='auto', out=out)