remove LU decomposition again

JoshuaLampert · Dec 11, 2024 · ca345a5 · ca345a5
1 parent f017619
commit ca345a5
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Showing 3 changed files with 3 additions and 68 deletions.
diff --git a/src/DispersiveShallowWater.jl b/src/DispersiveShallowWater.jl
@@ -20,7 +20,7 @@ using DiffEqBase: DiffEqBase, SciMLBase, terminate!
 using FastBroadcast: @..
 using Interpolations: Interpolations, linear_interpolation
 using LinearAlgebra: mul!, ldiv!, I, Diagonal, Symmetric, diag,
-                     lu, lu!, cholesky, cholesky!, issuccess
+                     lu, cholesky, cholesky!, issuccess
 using PolynomialBases: PolynomialBases
 using Printf: @printf, @sprintf
 using RecipesBase: RecipesBase, @recipe, @series

diff --git a/src/equations/equations.jl b/src/equations/equations.jl
@@ -567,7 +567,7 @@ function solve_system_matrix!(dv, system_matrix, rhs,
         if issuccess(factorization)
             scale_by_mass_matrix!(rhs, D1)
             # see https://github.com/JoshuaLampert/DispersiveShallowWater.jl/issues/122
-            dv .= system_matrix \ rhs[2:(end - 1)]
+            dv .= factorization \ rhs[2:(end - 1)]
         else
             # The factorization may fail if the time step is too large
             # and h becomes negative.
@@ -581,13 +581,6 @@ function solve_system_matrix!(dv, system_matrix, rhs,
     return nothing
 end
 
-# Svärd-Kalisch equations for reflecting boundary conditions uses LU factorization
-function solve_system_matrix_lu!(dv, system_matrix_lu, ::SvaerdKalischEquations1D, cache)
-    (; factorization_lu) = cache
-    lu!(factorization_lu, system_matrix_lu)
-    ldiv!(factorization_lu, dv)
-end
-
 function solve_system_matrix!(dv, system_matrix, ::Union{BBMEquation1D, BBMBBMEquations1D})
     ldiv!(system_matrix, dv)
 end

diff --git a/src/equations/svaerd_kalisch_1d.jl b/src/equations/svaerd_kalisch_1d.jl
@@ -223,13 +223,6 @@ function assemble_system_matrix!(cache, h,
     return Symmetric(Diagonal((@view M_h[2:(end - 1)])) + minus_MD1betaD1)
 end
 
-function assemble_system_matrix_lu!(cache, h,
-                                    ::SvaerdKalischEquations1D,
-                                    ::BoundaryConditionReflecting)
-    (; D1betaD1d) = cache
-    return Diagonal((@view h[2:(end - 1)])) - D1betaD1d
-end
-
 function create_cache(mesh, equations::SvaerdKalischEquations1D,
                       solver, initial_condition,
                       boundary_conditions::BoundaryConditionPeriodic,
@@ -333,15 +326,10 @@ function create_cache(mesh, equations::SvaerdKalischEquations1D,
        D1 isa UniformCoupledOperator
         D1_central = D1
         D1mat = sparse(D1_central)
-        D1betaD1d = sparse(D1mat * Diagonal(beta_hat) * D1mat * Pd)[2:(end - 1), :]
         minus_MD1betaD1 = sparse(D1mat' * Diagonal(M_beta) * D1mat * Pd)[2:(end - 1), :]
         system_matrix = let cache = (; D1, M_h, minus_MD1betaD1)
             assemble_system_matrix!(cache, h, equations, boundary_conditions)
         end
-        system_matrix_lu = let cache = (; D1betaD1d)
-            assemble_system_matrix_lu!(cache, h,
-                                       equations, boundary_conditions)
-        end
     elseif D1 isa UpwindOperators
         D1_central = D1.central
         D1mat_minus = sparse(D1.minus)
@@ -354,9 +342,7 @@ function create_cache(mesh, equations::SvaerdKalischEquations1D,
         throw(ArgumentError("unknown type of first-derivative operator: $(typeof(D1))"))
     end
     factorization = cholesky(system_matrix)
-    factorization_lu = lu(system_matrix_lu)
-    cache = (; factorization, factorization_lu, minus_MD1betaD1, D1betaD1d, D, h, hv, b,
-             eta_x, v_x,
+    cache = (; factorization, minus_MD1betaD1, D, h, hv, b, eta_x, v_x,
              h_v_x, hv2_x, beta_hat, D1_central, D1, M_h)
     return cache
 end
@@ -510,50 +496,6 @@ function rhs!(dq, q, t, mesh, equations::SvaerdKalischEquations1D,
     return nothing
 end
 
-function rhs_lu!(dq, q, t, mesh, equations::SvaerdKalischEquations1D,
-                 initial_condition, boundary_conditions::BoundaryConditionReflecting,
-                 source_terms, solver, cache)
-    # When constructing the `cache`, we assert that alpha and gamma are zero.
-    # We use this explicitly in the code below.
-    (; D, h, hv, b, eta_x, v_x, h_v_x, hv2_x, tmp1, D1_central, D1) = cache
-
-    g = gravity_constant(equations)
-    eta, v = q.x
-    deta, dv, dD = dq.x
-    fill!(dD, zero(eltype(dD)))
-
-    @trixi_timeit timer() "deta hyperbolic" begin
-        @.. b = equations.eta0 - D
-        @.. h = eta - b
-        @.. hv = h * v
-
-        mul!(deta, D1_central, -hv)
-    end
-
-    # split form
-    @trixi_timeit timer() "dv hyperbolic" begin
-        mul!(eta_x, D1_central, eta)
-        mul!(v_x, D1_central, v)
-        mul!(h_v_x, D1_central, hv)
-        @.. tmp1 = hv * v
-        mul!(hv2_x, D1_central, tmp1)
-        @.. dv = -(0.5 * (hv2_x + hv * v_x - v * h_v_x) +
-                   g * h * eta_x)
-    end
-
-    @trixi_timeit timer() "source terms" calc_sources!(dq, q, t, source_terms, equations,
-                                                       solver)
-    @trixi_timeit timer() "assemble system matrix" begin
-        system_matrix_lu = assemble_system_matrix_lu!(cache, h, equations, boundary_conditions)
-    end
-    @trixi_timeit timer() "solving elliptic system" begin
-        solve_system_matrix_lu!((@view dv[2:(end - 1)]), system_matrix_lu, equations, cache)
-        dv[1] = dv[end] = zero(eltype(dv))
-    end
-
-    return nothing
-end
-
 # The modified entropy/energy takes the whole `q` for every point in space
 """
     DispersiveShallowWater.energy_total_modified!(e, q_global, equations::SvaerdKalischEquations1D, cache)