Add DDETST problems and restructure existing DDE problems

src/DiffEqProblemLibrary.jl

@@ -19,7 +19,7 @@ end # module
 module DDEProblemLibrary
 function importddeproblems()
   @isdefined(prob_dde_1delay) ||
-  include(joinpath(@__DIR__, "dde_premade_problems.jl"));
+  include(joinpath(@__DIR__, "dde/dde_premade_problems.jl"));
   nothing
 end
 end # module

src/dde/constant_delays.jl

@@ -0,0 +1,358 @@
+# Helper function for changing initial value and time type of the following DDEs
+
+"""
+    remake_dde_constant_u0_tType(prob::DDEProblem, u₀, tType)
+
+Create a new delay differential problem by replacing the initial state of problem `prob`
+with `u0` and setting the type of time `t` to `tType`.
+
+This function makes special assumptions about the structure of `prob` and is intended to be
+used for all problems of name `prob_dde_constant_*` in `DDEProblemLibrary`. The functions of
+these delay differential equation problems with constant delays are purposefully
+implemented such that they work for arbitrary types of state `u` and time `t`, and hence in
+particular for number types with units. The element type of `u` is saved as parameter `p` to
+ensure that the return type of the history functions is correct (which are functions of `p`
+but not of `u`).
+"""
+function remake_dde_constant_u0_tType(prob::DDEProblem, u₀, tType)
+  remake(prob; u0 = u₀, tspan = tType.(prob.tspan), p = eltype(u₀),
+         constant_lags = tType.(prob.constant_lags))
+end
+
+# Single constant delay
+
+## Short time span
+
+### In-place function
+
+@doc raw"""
+    prob_dde_constant_1delay_ip
+
+Delay differential equation
+
+```math
+u'(t) = -u(t - 1)
+```
+
+for ``t \in [0, 1]`` with history function ``\phi(t) = 0`` if ``t < 0`` and ``\phi(0) = 1``.
+
+# Solution
+
+The analytical solution for ``t \in [0, 10]`` can be obtained by the method of steps and
+is provided in this implementation.
+"""
+const prob_dde_constant_1delay_ip = let
+  function f(du, u, h, p, t)
+    e = oneunit(t)
+    du[1] = - h(p, t - e; idxs = 1) * inv(e)
+
+    nothing
+  end
+
+  # history function of the first component
+  function h(p, t; idxs = 1)
+    idxs == 1 || error("history function is only implemented for the first component")
+    t ≤ zero(t) || error("history function is only implemented for t ≤ 0")
+
+    p === nothing ? zero(t) : zero(p)
+  end
+
+  # only valid for specific history function
+  function f_analytic(u₀, p, t)
+    z = t * inv(oneunit(t))
+    0 ≤ z ≤ 10 || error("analytical solution is only implemented for t ∈ [0, 10]")
+
+    if z < 1
+      copy(u₀)
+    else
+      if z < 2
+        c = @evalpoly(z, 2, -1)
+      elseif z < 3
+        c = @evalpoly(z, 4, -3, 1//2)
+      elseif z < 4
+        c = @evalpoly(z, 17//2, -15//2, 2, -1//6)
+      elseif z < 5
+        c = @evalpoly(z, 115//6, -109//6, 6, -5//6, 1//24)
+      elseif z < 6
+        c = @evalpoly(z, 1085//24, -1061//24, 197//12, -35//12, 1//4, -1//120)
+      elseif z < 7
+        c = @evalpoly(z, 13201//120, -13081//120, 521//12, -107//12, 1, -7//120, 1//720)
+      elseif z < 8
+        c = @evalpoly(z, 39371//144, -39227//144, 27227//240, -3685//144, 487//144,
+                      -21//80, 1//90, -1//5040)
+      elseif z < 9
+        c = @evalpoly(z, 1158379//1680, -1156699//1680, 212753//720, -51193//720,
+                      1511//144, -701//720, 1//18, -1//560, 1//40320)
+      else
+        c = @evalpoly(z, 23615939//13440, -23602499//13440, 7761511//10080,
+                      -279533//1440, 89269//2880, -1873//576, 323//1440, -11//1120,
+                      1//4032, -1//362880)
+      end
+
+      c .* u₀
+    end
+  end
+
+  DDEProblem(DDEFunction(f, analytic=f_analytic), [1.0], h, (0.0, 10.0), typeof(1.0);
+             constant_lags = [1])
+end
+
+### Out-of-place function
+
+"""
+    prob_dde_constant_1delay_oop
+
+Same delay differential equation as [`prob_dde_constant_1delay_ip`](@ref), but purposefully
+implemented with an out-of-place function.
+"""
+const prob_dde_constant_1delay_oop = let
+  function f(u, h, p, t)
+    e = oneunit(t)
+    .- h(p, t - e) .* inv(e)
+  end
+
+  # vectorized history function
+  function h(p, t)
+    t ≤ zero(t) || error("history function is only implemented for t ≤ 0")
+
+    p === nothing ? [zero(t)] : [zero(p)]
+  end
+
+  DDEProblem(DDEFunction(f, analytic=prob_dde_constant_1delay_ip.f.analytic), [1.0], h,
+             (0.0, 10.0), typeof(1.0); constant_lags = [1])
+end
+
+### Scalar function
+
+"""
+    prob_dde_constant_1delay_scalar
+
+Same delay differential equation as [`prob_dde_constant_1delay_ip`](@ref), but purposefully
+implemented with a scalar function.
+"""
+const prob_dde_constant_1delay_scalar = let
+  # scalar history function
+  function h(p, t)
+    t ≤ zero(t) || error("history function is only implemented for t ≤ 0")
+
+    p === nothing ? zero(t) : zero(p)
+  end
+
+  DDEProblem(prob_dde_constant_1delay_oop.f, 1.0, h, (0.0, 10.0), typeof(1.0);
+             constant_lags = [1])
+end
+
+## Long time span
+
+### In-place function
+
+@doc raw"""
+    prob_dde_constant_1delay_long_ip
+
+Delay differential equation
+
+```math
+u'(t) = u(t) - u(t - 1/5)
+```
+
+for ``t \in [0, 100]`` with history function ``\phi(t) = 0`` if ``t < 0`` and
+``\phi(0) = 1``.
+"""
+const prob_dde_constant_1delay_long_ip = let
+  function f(du, u, h, p, t)
+    T = typeof(t)
+    du[1] = (u[1] - h(p, t - T(1/5); idxs = 1)) * inv(oneunit(t))
+
+    nothing
+  end
+
+  DDEProblem(f, [1.0], prob_dde_constant_1delay_ip.h, (0.0, 100.0), typeof(1.0);
+             constant_lags = [1/5])
+end
+
+### Out-of-place function
+
+"""
+    prob_dde_constant_1delay_long_oop
+
+Same delay differential equation as [`prob_dde_constant_1delay_long_ip`](@ref), but
+purposefully implemented with an out-of-place function.
+"""
+const prob_dde_constant_1delay_long_oop = let
+  function f(u, h, p, t)
+    T = typeof(t)
+    (u .- h(p, t - T(1/5))) .* inv(oneunit(t))
+  end
+
+  DDEProblem(f, [1.0], prob_dde_constant_1delay_oop.h, (0.0, 100.0), typeof(1.0);
+             constant_lags = [1/5])
+end
+
+### Scalar function
+
+"""
+    prob_dde_constant_1delay_long_scalar
+
+Same delay differential equation as [`prob_dde_constant_1delay_long_ip`](@ref), but
+purposefully implemented with a scalar function.
+"""
+const prob_dde_constant_1delay_long_scalar =
+  DDEProblem(prob_dde_constant_1delay_long_oop.f, 1.0, prob_dde_constant_1delay_scalar.h,
+             (0.0, 100.0), typeof(1.0); constant_lags = [1/5])
+
+# Two constant delays
+
+## Short time span
+
+### In-place function
+
+@doc raw"""
+    prob_dde_constant_2delays_ip
+
+Delay differential equation
+
+```math
+u'(t) = -u(t - 1/3) - u(t - 1/5)
+```
+
+for ``t \in [0, 1]`` with history function ``\phi(t) = 0`` if ``t < 0`` and ``\phi(0) = 1``.
+
+# Solution
+
+The analytical solution for ``t \in [0, 10]`` can be obtained by the method of steps and
+is provided in this implementation.
+"""
+const prob_dde_constant_2delays_ip = let
+  function f(du, u, h, p, t)
+    T = typeof(t)
+    du[1] = - (h(p, t - T(1/3); idxs = 1) + h(p, t - T(1/5); idxs = 1)) * inv(oneunit(t))
+
+    nothing
+  end
+
+  # only valid for specific history function
+  function f_analytic(u₀, p, t)
+    z = t * inv(oneunit(t))
+    0 ≤ z ≤ 1 || error("analytical solution is only implemented for t ∈ [0, 1]")
+
+    if z < 1/5
+      copy(u₀)
+    else
+      if z < 1/3
+        c = @evalpoly(z, 6//5, -1)
+      elseif z < 2/5
+        c = @evalpoly(z, 23//15, -2)
+      elseif z < 8/15
+        c = @evalpoly(z, 121//75, -12//5, 1//2)
+      elseif z < 3/5
+        c = @evalpoly(z, 427//225, -52//15, 3//2)
+      elseif z < 2/3
+        c = @evalpoly(z, 4351//2250, -547//150, 9//5, -1//6)
+      elseif z < 11/15
+        c = @evalpoly(z, 539//250, -647//150, 23//10, -1//6)
+      elseif z < 4/5
+        c = @evalpoly(z, 7942//3375, -128//25, 17//5, -2//3)
+      elseif z < 13/15
+        c = @evalpoly(z, 39998//16875, -1952//375, 89//25, -4//5, 1//24)
+      elseif z < 14/15
+        c = @evalpoly(z, 10109//3750, -1583//250, 243//50, -13//10, 1//24)
+      else
+        c = @evalpoly(z, 171449//60750, -139199//20250, 2579//450, -173//90, 5//24)
+      end
+
+      c .* u₀
+    end
+  end
+
+  DDEProblem(DDEFunction(f, analytic = f_analytic), [1.0], prob_dde_constant_1delay_ip.h,
+             (0.0, 1.0), typeof(1.0); constant_lags = [1/3, 1/5])
+end
+
+### Out-of-place function
+
+"""
+    prob_dde_constant_2delays_oop
+
+Same delay differential equation as [`prob_dde_constant_2delays_ip`](@ref), but purposefully
+implemented with an out-of-place function.
+"""
+const prob_dde_constant_2delays_oop = let
+  function f(u, h, p, t)
+    T = typeof(t)
+    .- (h(p, t - T(1/3)) .+  h(p, t - T(1/5))) .* inv(oneunit(t))
+  end
+
+  DDEProblem(DDEFunction(f, analytic = prob_dde_constant_2delays_ip.f.analytic), [1.0],
+             prob_dde_constant_1delay_oop.h, (0.0, 1.0), typeof(1.0);
+             constant_lags = [1/3, 1/5])
+end
+
+### Scalar function
+
+"""
+    prob_dde_constant_2delays_scalar
+
+Same delay differential equation as [`prob_dde_constant_2delays_ip`](@ref), but purposefully
+implemented with a scalar function.
+"""
+const prob_dde_constant_2delays_scalar =
+  DDEProblem(prob_dde_constant_2delays_oop.f, 1.0, prob_dde_constant_1delay_scalar.h,
+             (0.0, 1.0), typeof(1.0); constant_lags = [1/3, 1/5])
+
+## Long time span
+
+### In-place function
+
+@doc raw"""
+    prob_dde_constant_2delays_long_ip
+
+Delay differential equation
+
+```math
+u'(t) = - u(t - 1/3) - u(t - 1/5)
+```
+
+for ``t \in [0, 100]`` with history function ``\phi(t) = 0`` if ``t < 0`` and
+``\phi(0) = 1``.
+"""
+const prob_dde_constant_2delays_long_ip = let
+  function f(du, u, h, p, t)
+    T = typeof(t)
+    du[1] = - (h(p, t - T(1/3); idxs = 1) + h(p, t - T(1/5); idxs = 1)) * inv(oneunit(t))
+
+    nothing
+  end
+
+  DDEProblem(f, [1.0], prob_dde_constant_1delay_ip.h, (0.0, 100.0), typeof(1.0);
+             constant_lags = [1/3, 1/5])
+end
+
+### Not in-place function
+
+"""
+    prob_dde_constant_2delays_long_oop
+
+Same delay differential equation as [`prob_dde_constant_2delays_long_ip`](@ref), but
+purposefully implemented with an out-of-place function.
+"""
+const prob_dde_constant_2delays_long_oop = let
+  function f(u, h, p, t)
+    T = typeof(t)
+    .- (h(p, t - T(1/3)) .+ h(p, t - T(1/5))) .* inv(oneunit(t))
+  end
+
+  DDEProblem(f, [1.0], prob_dde_constant_1delay_oop.h, (0.0, 100.0), typeof(1.0);
+             constant_lags = [1/3, 1/5])
+end
+
+#### Scalar function
+
+"""
+    prob_dde_constant_2delays_long_scalar
+
+Same delay differential equation as [`prob_dde_constant_2delays_long_ip`](@ref), but
+purposefully implemented with a scalar function.
+"""
+const prob_dde_constant_2delays_long_scalar =
+  DDEProblem(prob_dde_constant_2delays_long_oop.f, 1.0, prob_dde_constant_1delay_scalar.h,
+             (0.0, 100.0), typeof(1.0); constant_lags = [1/3, 1/5])