Tools¶

Version query¶

modepy.version.VERSION¶: A tuple like (2013, 1, 1) indicating modepy’s version.

modepy.version.VERSION_TEXT¶: A textual representation of the modepy version.

Interpolation matrices¶

modepy.vandermonde(functions, nodes)[source]¶

Return a (generalized) Vandermonde matrix.

The Vandermonde Matrix is given by $V_{i,j} := f_j(x_i)$ where functions is the list of $f_j$ and nodes is the array of $x_i$, shaped as (d, npts), where d is the number of dimensions and npts is the number of nodes.

functions are allowed to return tuple instances. In this case, a tuple of matrices is returned–i.e. this function works directly on modepy.Basis.gradients() and returns a tuple of matrices.

Vandermonde matrices are very useful to concisely express interpolation. For instance, one may use the inverse $V^{-1}$ of a Vandermonde matrix $V$ to map nodal values (i.e. point values at the nodes corresponding to $V$) into modal (i.e. basis) coefficients. $V$ itself maps modal coefficients to nodal values. This allows easy resampling:

modepy.resampling_matrix(basis, new_nodes, old_nodes, least_squares_ok=False)[source]¶

Return a matrix that maps nodal values on old_nodes onto nodal values on new_nodes.

Parameters:

basis – A sequence of basis functions accepting arrays of shape (dims, npts), like those returned by modepy.orthonormal_basis_for_space().
new_nodes – An array of shape (dims, n_new_nodes)
old_nodes – An array of shape (dims, n_old_nodes)
least_squares_ok – If False, then nodal values at old_nodes are required to determine the interpolant uniquely, i.e. the Vandermonde matrix must be square. If True, then a point-wise least-squares best-approximant is used (by ways of the pseudo-inverse of the Vandermonde matrix).

Vandermonde matrices also obey the following relationship useful for obtaining point interpolants:

\[V^T [\text{interpolation coefficients to point $x$}] = \phi_i(x),\]

where $(\phi_i)_i$ is the basis of functions underlying $V$.

modepy.inverse_mass_matrix(basis, nodes)[source]¶: Return a matrix $A=M^{-1}$, which is the inverse of the one returned by mass_matrix().

Added in version 2015.1.

modepy.mass_matrix(basis, nodes)[source]¶

Return a mass matrix $M$, which obeys

\[M_{ij} = \int_\triangle \phi_i(x) \phi_j(x) dx = (V^{-T} V^{-1})_{ij}.\]

Parameters:: basis – assumed to be an orthonormal basis with respect to the $L^2$ inner product.

Added in version 2014.1.

modepy.modal_mass_matrix_for_face(face: Face, face_quad: Quadrature, trial_functions, test_functions)[source]¶

Using the quadrature face_quad, provide a matrix $M_f$ that satisfies:

\[\displaystyle {(M_f)}_{ij} \approx \int_F \phi_i(r) \psi_j(r) dr,\]

where $\phi_i$ are the (volume) Lagrange basis functions obtained from test_functions at volume_nodes, and $\psi_j$ are the (surface) trial_functions.

Added in version 2020.3.

modepy.nodal_mass_matrix_for_face(face: Face, face_quad: Quadrature, trial_functions, test_functions, volume_nodes, face_nodes)[source]¶

Using the quadrature face_quad, provide a matrix $M_f$ that satisfies:

\[\displaystyle {(M_f)}_{ij} \approx \int_F \phi_i(r) \psi_j(r) dr,\]

where $\phi_i$ are the (volume) Lagrange basis functions obtained from test_functions at volume_nodes, and $\psi_j$ are the (surface) Lagrange basis functions obtained from trial_functions at face_nodes.

Added in version 2020.3.

modepy.nodal_quad_mass_matrix_for_face(face: Face, face_quad: Quadrature, test_functions, volume_nodes)[source]¶

Using the quadrature face_quad, provide a matrix $M_f$ that satisfies:

\[\displaystyle (M_f \boldsymbol u)_i = \sum_j w_j \phi_i(r_j) u_j,\]

where $\phi_i$ are the (volume) Lagrange basis functions obtained from test_functions at volume_nodes, and $w_i$ and $r_i$ are the weights and nodes from face_quad.

Added in version 2021.2.

Differentiation is also convenient to express by using $V^{-1}$ to obtain modal values and then using a Vandermonde matrix for the derivatives of the basis to return to nodal values.

modepy.differentiation_matrices(basis, grad_basis, nodes, from_nodes=None)[source]¶

Return matrices carrying out differentiation on nodal values in the $(r,s,t)$ unit directions. (See Coordinates on the triangle and Coordinates on the tetrahedron.)

Parameters:

basis – A sequence of basis functions accepting arrays of shape (dims, npts), like those returned by modepy.Basis.functions().
grad_basis – A sequence of functions returning the gradients of basis, like those in modepy.Basis.gradients.
nodes – An array of shape (dims, n_nodes)
from_nodes – An array of shape (dims, n_from_nodes). If None, assumed to be the same as nodes.

Returns:

If grad_basis returned tuples (i.e. in 2D and 3D), returns a tuple of length dims containing differentiation matrices. If not, returns just one differentiation matrix.

Changed in version 2013.4: Added from_nodes.

modepy.diff_matrix_permutation(node_tuples, ref_axis)[source]¶

Return a numpy array permutation of integers so that:

diff_matrices[ref_axis] == diff_matrices[0][permutation][:, permutation]

Added in version 2020.1.

Modal decay/residual¶

Estimate the smoothness of a function represented in a basis returned by modepy.orthonormal_basis_for_space().

The method implemented in this module follows this article:

A. Kloeckner, T. Warburton, and J. S. Hesthaven. “Viscous Shock Capturing in a Time-Explicit Discontinuous Galerkin Method”. Mathematical Modelling of Natural Phenomena 6, No. 3 (May 16, 2011): 57-83. http://dx.doi.org/10.1051/mmnp/20116303 http://arxiv.org/abs/1102.3190

Added in version 2013.2.

modepy.modal_decay.simplex_interp_error_coefficient_estimator_matrix(unit_nodes: ndarray, order: int, n_tail_orders: int) → ndarray[source]¶

Return a matrix $C$ that, when multiplied by a vector of nodal values, yields the coeffiicients belonging to the basis functions of the n_tail_orders highest orders.

The 2-norm of the resulting coefficients can be used as an estimate of the interpolation error.

Added in version 2018.1.

modepy.modal_decay.fit_modal_decay(coeffs: ndarray, dims: int, n: int, ignored_modes: int = 1) → Tuple[ndarray, ndarray][source]¶

Fit a curve to the modal decay on each element.

Parameters:

coeffs – an array of shape (num_elements, num_modes) containing modal coefficients of the functions to be analyzed.
dims – number of dimensions.
ignored_modes – the number of modal coefficients to ignore at the beginning. The default value of ‘1’ ignores the constant.

Returns:

a tuple (expn, constant) of arrays of length num_elements, where the modal decay is fit to the curve constant * total_degree**exponent. -exponent-1 can be used as a rough indicator of how many continuous derivatives the underlying function possesses.

modepy.modal_decay.estimate_relative_expansion_residual(coeffs: ndarray, dims: int, n: int, ignored_modes: int = 1) → ndarray[source]¶

Use the modal fit to estimate the relative residual of the expansion. The arguments to this function exactly match fit_modal_decay().

Returns:: An array of estimates of the fraction of the $L^2$ norm contained in the (unrepresented) tail of

An idea like this is described in this article:

H. Feng and C. Mavriplis, “Adaptive Spectral Element Simulations of Thin Premixed Flame Sheet Deformations”, Journal of Scientific Computing, Volume 17, Nr. 1, S. 385-395, Dec. 2002. http://dx.doi.org/10.1023/A:1015137722700

For this function, however, the decay curve is fitted using the Kloeckner/Warburton/Hesthaven technique (see above).

Transformations between coordinate systems on the simplex¶

All of these expect and return arrays of shape (dims, npts).

modepy.tools.equilateral_to_unit(equi)[source]¶

modepy.tools.barycentric_to_unit(bary)[source]¶

Parameters:: bary – shaped (dims+1, npoints)

modepy.tools.unit_to_barycentric(unit)[source]¶

Parameters:: unit – shaped (dims,npoints)

modepy.tools.barycentric_to_equilateral(bary)[source]¶

Interpolation quality¶

modepy.tools.estimate_lebesgue_constant(n: int, nodes: ndarray, shape: Shape | None = None, *, visualize: bool = False) → float[source]¶

Estimate the Lebesgue constant of the nodes at polynomial order n.

Parameters:

nodes – an array of shape (dim, nnodes) as returned by modepy.warp_and_blend_nodes().
shape – a Shape.
visualize – visualize the function that gives rise to the returned Lebesgue constant. (2D only for now)

Returns:

the Lebesgue constant, a scalar.

Added in version 2013.2.

Changed in version 2020.2: domain parameter was added with support for nodes on the unit hypercube (i.e. unit square in 2D and unit cube in 3D).

Changed in version 2020.3: Renamed domain to shape.

DOF arrays of tensor product discretizations¶

modepy.tools.reshape_array_for_tensor_product_space(space: TensorProductSpace, ary: ReshapeableT, axis=-1) → ReshapeableT[source]¶

Return a reshaped view of ary that exposes the tensor product nature of the space. Axis number axis of ary must index coefficients corresponding to a tensor-product-structured basis (e.g. modal or nodal coefficients).

Parameters:

ary – an array with last dimension having a length matching the space_dim of space.
result – ary reshaped with axis number axis replaced by a tuple of dimensions matching the dimensions of the spaces making up the tensor product. Variation of the represented function along a given dimension will be represented by variation of array entries along the corresponding array axis.

modepy.tools.unreshape_array_for_tensor_product_space(space: TensorProductSpace, ary: ReshapeableT, axis=-1) → ReshapeableT[source]¶: Undoes the effect of reshape_array_for_tensor_product_space(), given the same space and axis.

Types used in documentation¶

class modepy.tools.ReshapeableT¶: An array-like protocol that supports finding the shape and reshaping.