added utils test

Author: xtalax

test/runtests.jl

@@ -17,6 +17,7 @@ if GROUP == "All" || GROUP == "MOLFiniteDifference"
     @time @safetestset "MOLFiniteDifference Interface: 1D HigherOrder" begin include("pde_systems/MOL_1D_HigherOrder.jl") end
     @time @safetestset "MOLFiniteDifference Interface: 1D Partial DAE" begin include("pde_systems/MOL_1D_PDAE.jl") end
     @time @safetestset "MOLFiniteDifference Interface: Stationary Nonlinear Problems" begin include("pde_systems/MOL_NonlinearProblem.jl") end
+    @time @safetestset "MOLFiniteDifference Utils" begin include("utils_test.jl") end
 end
 
 end

test/utils_test.jl

@@ -0,0 +1,74 @@
+using MethodOfLines, Test, ModelingToolkit
+
+@testset "count differentials 1D" begin
+    @parameters t x
+    @variables u(..)
+    Dt = Differential(t)
+
+    Dx = Differential(x)
+    eq  = Dt(u(t,x)) ~ -Dx(u(t,x))
+    @test first(DiffEqOperators.differential_order(eq.rhs, x.val)) == 1
+    @test isempty(DiffEqOperators.differential_order(eq.rhs, t.val))
+    @test first(DiffEqOperators.differential_order(eq.lhs, t.val)) == 1
+    @test isempty(DiffEqOperators.differential_order(eq.lhs, x.val))
+
+    Dxx = Differential(x)^2
+    eq  = Dt(u(t,x)) ~ Dxx(u(t,x))
+    @test first(DiffEqOperators.differential_order(eq.rhs, x.val)) == 2
+    @test isempty(DiffEqOperators.differential_order(eq.rhs, t.val))
+    @test first(DiffEqOperators.differential_order(eq.lhs, t.val)) == 1
+    @test isempty(DiffEqOperators.differential_order(eq.lhs, x.val))
+
+    Dxxxx = Differential(x)^4
+    eq  = Dt(u(t,x)) ~ -Dxxxx(u(t,x))
+    @test first(DiffEqOperators.differential_order(eq.rhs, x.val)) == 4
+    @test isempty(DiffEqOperators.differential_order(eq.rhs, t.val))
+    @test first(DiffEqOperators.differential_order(eq.lhs, t.val)) == 1
+    @test isempty(DiffEqOperators.differential_order(eq.lhs, x.val))
+end
+
+@testset "count differentials 2D" begin
+    @parameters t x y
+    @variables u(..)
+    Dxx = Differential(x)^2
+    Dyy = Differential(y)^2
+    Dt = Differential(t)
+
+    eq  = Dt(u(t,x,y)) ~ Dxx(u(t,x,y)) + Dyy(u(t,x,y))
+    @test first(DiffEqOperators.differential_order(eq.rhs, x.val)) == 2
+    @test first(DiffEqOperators.differential_order(eq.rhs, y.val)) == 2
+    @test isempty(DiffEqOperators.differential_order(eq.rhs, t.val))
+    @test first(DiffEqOperators.differential_order(eq.lhs, t.val)) == 1
+    @test isempty(DiffEqOperators.differential_order(eq.lhs, x.val))
+    @test isempty(DiffEqOperators.differential_order(eq.lhs, y.val))
+end
+
+@testset "count with mixed terms" begin
+    @parameters t x y
+    @variables u(..)
+    Dxx = Differential(x)^2
+    Dyy = Differential(y)^2
+    Dx = Differential(x)
+    Dy = Differential(y)
+    Dt = Differential(t)
+
+    eq  = Dt(u(t,x,y)) ~ Dxx(u(t,x,y)) + Dyy(u(t,x,y)) + Dx(Dy(u(t,x,y)))
+    @test DiffEqOperators.differential_order(eq.rhs, x.val) == Set([2, 1])
+    @test DiffEqOperators.differential_order(eq.rhs, y.val) == Set([2, 1])
+end
+
+@testset "Kuramoto–Sivashinsky equation" begin
+    @parameters x, t
+    @variables u(..)
+    Dt = Differential(t)
+    Dx = Differential(x)
+    Dx2 = Differential(x)^2
+    Dx3 = Differential(x)^3
+    Dx4 = Differential(x)^4
+
+    α = 1
+    β = 4
+    γ = 1
+    eq = Dt(u(x,t)) + u(x,t)*Dx(u(x,t)) + α*Dx2(u(x,t)) + β*Dx3(u(x,t)) + γ*Dx4(u(x,t)) ~ 0
+    @test DiffEqOperators.differential_order(eq.lhs, x.val) == Set([4, 3, 2, 1])
+end