Commit 9ee520a4 authored by Juan Ignacio Polanco's avatar Juan Ignacio Polanco

Document galerkin_matrix

parent acba7fd1
......@@ -114,7 +114,7 @@ end
[MatrixType = SparseMatrixCSC{Float64}];
Ndiff::Val = Val(0),
clip_threshold = eps(eltype(MatrixType)),
galerkin_matrix(B::BSplineBasis, [MatrixType = BandedMatrix{Float64}])
Compute Galerkin mass matrix.
M[i, j] = ⟨ bᵢ(x), bⱼ(x) ⟩ for i = 1:N and j = 1:N,
where `bᵢ` is the i-th B-spline and `N = length(B)` is the number of B-splines
in the basis `B`.
Here, ⟨⋅,⋅⟩ is the [L² inner
between functions.
Note that the Galerkin matrix is symmetric, positive definite and banded,
with `k + 1` and `k + 2` for `k` even and odd, respectively.
This function always returns a
view of an underlying matrix.
By default, the underlying matrix holding the data is a `BandedMatrix` that
defines the upper part of the symmetric matrix.
Other types of container are also supported, including regular sparse matrices
(`SparseMatrixCSC`) and dense arrays (`Matrix`).
function galerkin_matrix(
::Type{M} = BandedMatrix{Float64}
......@@ -10,6 +36,9 @@ end
allocate_galerkin_matrix(::Type{M}, N, k) where {M <: AbstractMatrix} =
Symmetric(M(undef, N, N))
allocate_galerkin_matrix(::Type{SparseMatrixCSC{T}}, N, k) where {T} =
spzeros(T, N, N)
function allocate_galerkin_matrix(::Type{M}, N, k) where {M <: BandedMatrix}
# The upper/lower bandwidths are:
# - for even k: Nb = k / 2 (total = k + 1 bands)
......@@ -20,6 +49,19 @@ function allocate_galerkin_matrix(::Type{M}, N, k) where {M <: BandedMatrix}
galerkin_matrix!(S::Symmetric, B::BSplineBasis)
Fill preallocated Galerkin mass matrix.
It is assumed that the `Symmetric` view looks at the data in the upper part of
its parent. In other words, it was constructed with the `uplo = :U` option,
which is the default in Julia. See the [Julia
for details.
See also [`galerkin_matrix`](@ref).
function galerkin_matrix!(S::Symmetric, B::BSplineBasis)
N = size(S, 1)
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