Revisiting Boundary Value Problems

Project.toml

@@ -1,7 +1,7 @@
 name = "SciMLBase"
 uuid = "0bca4576-84f4-4d90-8ffe-ffa030f20462"
 authors = ["Chris Rackauckas <[email protected]> and contributors"]
-version = "1.98.1"
+version = "1.98.2"  # Remember to make it 2.0.0
 
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"

src/problems/bvp_problems.jl

@@ -3,6 +3,11 @@
 """
 struct StandardBVProblem end
 
+"""
+$(TYPEDEF)
+"""
+struct TwoPointBVProblem end
+
 @doc doc"""
 
 Defines an BVP problem.
@@ -17,7 +22,7 @@
 \frac{du}{dt} = f(u,p,t)
 ```
 
-along with an implicit function `bc!` which defines the residual equation, where
+along with an implicit function `bc` which defines the residual equation, where
 
 ```math
 bc(u,p,t) = 0
@@ -36,22 +41,27 @@
 ### Constructors
 
 ```julia
-TwoPointBVProblem{isinplace}(f,bc!,u0,tspan,p=NullParameters();kwargs...)
-BVProblem{isinplace}(f,bc!,u0,tspan,p=NullParameters();kwargs...)
+TwoPointBVProblem{isinplace}(f,bc,u0,tspan,p=NullParameters();kwargs...)
+BVProblem{isinplace}(f,bc,u0,tspan,p=NullParameters();kwargs...)
 ```
 
 or if we have an initial guess function `initialGuess(t)` for the given BVP,
 we can pass the initial guess to the problem constructors:
 
 ```julia
-TwoPointBVProblem{isinplace}(f,bc!,initialGuess,tspan,p=NullParameters();kwargs...)
-BVProblem{isinplace}(f,bc!,initialGuess,tspan,p=NullParameters();kwargs...)
+TwoPointBVProblem{isinplace}(f,bc,initialGuess,tspan,p=NullParameters();kwargs...)
+BVProblem{isinplace}(f,bc,initialGuess,tspan,p=NullParameters();kwargs...)
 ```
 
-For any BVP problem type, `bc!` is the inplace function:
+For any BVP problem type, `bc` must be inplace if `f` is inplace. Otherwise it must be
+out-of-place.
+
+If the bvp is a StandardBVProblem (also known as a Multi-Point BV Problem) it must define
+either of the following functions
 
 ```julia
 bc!(residual, u, p, t)
+residual = bc(u, p, t)
 ```
 
 where `residual` computed from the current `u`. `u` is an array of solution values
@@ -61,6 +71,16 @@
 Note that all features of the `ODESolution` are present in this form.
 In both cases, the size of the residual matches the size of the initial condition.
 
+If the bvp is a TwoPointBVProblem it must define either of the following functions
+
+```julia
+bc!((resid_a, resid_b), (u_a, u_b), p)
+resid_a, resid_b = bc((u_a, u_b), p)
+```
+
+where `resid_a` and `resid_b` are the residuals at the two endpoints, `u_a` and `u_b` are
+the solution values at the two endpoints, and `p` are the parameters.
+
 Parameters are optional, and if not given, then a `NullParameters()` singleton
 will be used which will throw nice errors if you try to index non-existent
 parameters. Any extra keyword arguments are passed on to the solvers. For example,
@@ -88,16 +108,14 @@
     problem_type::PT
     kwargs::K
 
-    @add_kwonly function BVProblem{iip}(f::AbstractBVPFunction{iip}, bc, u0, tspan,
-        p = NullParameters(),
-        problem_type = StandardBVProblem();
-        kwargs...) where {iip}
+    @add_kwonly function BVProblem{iip}(f::AbstractBVPFunction{iip, TP}, bc, u0, tspan,
+        p = NullParameters(); kwargs...) where {iip, TP}
         _tspan = promote_tspan(tspan)
         warn_paramtype(p)
-        new{typeof(u0), typeof(_tspan), isinplace(f), typeof(p),
-            typeof(f), typeof(f.bc),
-            typeof(problem_type), typeof(kwargs)}(f, f.bc, u0, _tspan, p,
-            problem_type, kwargs)
+        problem_type = TP ? TwoPointBVProblem() : StandardBVProblem()
+        return new{typeof(u0), typeof(_tspan), iip, typeof(p), typeof(f), typeof(bc),
+            typeof(problem_type), typeof(kwargs)}(f, bc, u0, _tspan, p, problem_type,
+            kwargs)
     end
 
     function BVProblem{iip}(f, bc, u0, tspan, p = NullParameters(); kwargs...) where {iip}
@@ -107,52 +125,43 @@
 
 TruncatedStacktraces.@truncate_stacktrace BVProblem 3 1 2
 
-function BVProblem(f::AbstractBVPFunction, u0, tspan, p = NullParameters(); kwargs...)
-    BVProblem{isinplace(f)}(f, f.bc, u0, tspan, p; kwargs...)
+function BVProblem(f, bc, u0, tspan, p = NullParameters(); kwargs...)
+    iip = isinplace(f, 4)
+    return BVProblem{iip}(BVPFunction{iip}(f, bc), bc, u0, tspan, p; kwargs...)
 end
 
-function BVProblem(f, bc, u0, tspan, p = NullParameters(); kwargs...)
-    BVProblem(BVPFunction(f, bc), u0, tspan, p; kwargs...)
+function BVProblem(f::AbstractBVPFunction, u0, tspan, p = NullParameters(); kwargs...)
+    return BVProblem{isinplace(f)}(f, f.bc, u0, tspan, p; kwargs...)
 end
 
-"""
-$(TYPEDEF)
-"""
-struct TwoPointBVPFunction{bF}
-    bc::bF
+# This is mostly a fake stuct and isn't used anywhere
+# But we need it for function calls like TwoPointBVProblem{iip}(...) = ...
+struct TwoPointBVPFunction{iip} end
+
+@inline TwoPointBVPFunction(args...; kwargs...) = BVPFunction(args...; kwargs..., twopoint=true)
+@inline function TwoPointBVPFunction{iip}(args...; kwargs...) where {iip}
+    return BVPFunction{iip}(args...; kwargs..., twopoint=true)
 end
-TwoPointBVPFunction(; bc = error("No argument bc")) = TwoPointBVPFunction(bc)
-(f::TwoPointBVPFunction)(residual, ua, ub, p) = f.bc(residual, ua, ub, p)
-(f::TwoPointBVPFunction)(residual, u, p) = f.bc(residual, u[1], u[end], p)
 
-"""
-$(TYPEDEF)
-"""
-struct TwoPointBVProblem{iip} end
-function TwoPointBVProblem(f, bc, u0, tspan, p = NullParameters(); kwargs...)
-    iip = isinplace(f, 4)
-    TwoPointBVProblem{iip}(f, bc, u0, tspan, p; kwargs...)
+function TwoPointBVProblem(f, bc, u0, tspan, p = NullParameters();
+    bcresid_prototype=nothing, kwargs...)
+    return TwoPointBVProblem(TwoPointBVPFunction(f, bc; bcresid_prototype), u0, tspan, p;
+        kwargs...)
 end
-function TwoPointBVProblem{iip}(f, bc, u0, tspan, p = NullParameters();
-    kwargs...) where {iip}
-    BVProblem{iip}(f, TwoPointBVPFunction(bc), u0, tspan, p; kwargs...)
+function TwoPointBVProblem(f::AbstractBVPFunction{iip, twopoint}, u0, tspan,
+    p = NullParameters(); kwargs...) where {iip, twopoint}
+    @assert twopoint "`TwoPointBVProblem` can only be used with a `TwoPointBVPFunction`. Instead of using `BVPFunction`, use `TwoPointBVPFunction` or pass a kwarg `twopoint=true` during the construction of the `BVPFunction`."
+    return BVProblem{iip}(f, f.bc, u0, tspan, p; kwargs...)
 end
 
 # Allow previous timeseries solution
-function TwoPointBVProblem(f::AbstractODEFunction,
-    bc,
-    sol::T,
-    tspan::Tuple,
-    p = NullParameters()) where {T <: AbstractTimeseriesSolution}
-    TwoPointBVProblem(f, bc, sol.u, tspan, p)
+function TwoPointBVProblem(f::AbstractODEFunction, bc, sol::T, tspan::Tuple,
+    p = NullParameters(); kwargs...) where {T <: AbstractTimeseriesSolution}
+    return TwoPointBVProblem(f, bc, sol.u, tspan, p; kwargs...)
 end
 # Allow initial guess function for the initial guess
-function TwoPointBVProblem(f::AbstractODEFunction,
-    bc,
-    initialGuess,
-    tspan::AbstractVector,
-    p = NullParameters();
-    kwargs...)
+function TwoPointBVProblem(f::AbstractODEFunction, bc, initialGuess, tspan::AbstractVector,
+    p = NullParameters(); kwargs...)
     u0 = [initialGuess(i) for i in tspan]
-    TwoPointBVProblem(f, bc, u0, (tspan[1], tspan[end]), p)
+    return TwoPointBVProblem(f, bc, u0, (tspan[1], tspan[end]), p; kwargs...)
 end

src/scimlfunctions.jl

@@ -2124,8 +2124,7 @@
 """
 $(TYPEDEF)
 """
-abstract type AbstractBVPFunction{iip} <:
-              AbstractDiffEqFunction{iip} end
+abstract type AbstractBVPFunction{iip, twopoint} <: AbstractDiffEqFunction{iip} end
 
 @doc doc"""
     BVPFunction{iip,F,BF,TMM,Ta,Tt,TJ,BCTJ,JVP,VJP,JP,BCJP,SP,TW,TWt,TPJ,S,S2,S3,O,TCV,BCTCV} <: AbstractBVPFunction{iip,specialize}
@@ -2230,11 +2229,9 @@
 
 The fields of the BVPFunction type directly match the names of the inputs.
 """
-struct BVPFunction{iip, specialize, F, BF, TMM, Ta, Tt, TJ, BCTJ, JVP, VJP, JP,
-    BCJP, SP, TW, TWt,
-    TPJ,
-    S, S2, S3, O, TCV, BCTCV,
-    SYS} <: AbstractBVPFunction{iip}
+struct BVPFunction{iip, specialize, twopoint, F, BF, TMM, Ta, Tt, TJ, BCTJ, JVP, VJP,
+    JP, BCJP, BCRP, SP, TW, TWt, TPJ, S, S2, S3, O, TCV, BCTCV,
+    SYS} <: AbstractBVPFunction{iip, twopoint}
     f::F
     bc::BF
     mass_matrix::TMM
@@ -2246,6 +2243,7 @@
     vjp::VJP
     jac_prototype::JP
     bcjac_prototype::BCJP
+    bcresid_prototype::BCRP
     sparsity::SP
     Wfact::TW
     Wfact_t::TWt
@@ -3648,9 +3646,8 @@
                nothing,
     sys = __has_sys(f) ? f.sys : nothing,
     resid_prototype = __has_resid_prototype(f) ? f.resid_prototype : nothing) where {
-    iip,
-    specialize,
-}
+    iip, specialize}
+
     if mass_matrix === I && typeof(f) <: Tuple
         mass_matrix = ((I for i in 1:length(f))...,)
     end
@@ -3814,35 +3811,28 @@
         cons_expr, sys)
 end
 
-function BVPFunction{iip, specialize}(f, bc;
-    mass_matrix = __has_mass_matrix(f) ? f.mass_matrix :
-                  I,
+function BVPFunction{iip, specialize, twopoint}(f, bc;
+    mass_matrix = __has_mass_matrix(f) ? f.mass_matrix : I,
     analytic = __has_analytic(f) ? f.analytic : nothing,
     tgrad = __has_tgrad(f) ? f.tgrad : nothing,
     jac = __has_jac(f) ? f.jac : nothing,
     bcjac = __has_jac(bc) ? bc.jac : nothing,
     jvp = __has_jvp(f) ? f.jvp : nothing,
     vjp = __has_vjp(f) ? f.vjp : nothing,
-    jac_prototype = __has_jac_prototype(f) ?
-                    f.jac_prototype :
-                    nothing,
-    bcjac_prototype = __has_jac_prototype(bc) ?
-                      bc.jac_prototype :
-                      nothing,
-    sparsity = __has_sparsity(f) ? f.sparsity :
-               jac_prototype,
+    jac_prototype = __has_jac_prototype(f) ? f.jac_prototype : nothing,
+    bcjac_prototype = __has_jac_prototype(bc) ? bc.jac_prototype : nothing,
+    bcresid_prototype = nothing,
+    sparsity = __has_sparsity(f) ? f.sparsity : jac_prototype,
     Wfact = __has_Wfact(f) ? f.Wfact : nothing,
     Wfact_t = __has_Wfact_t(f) ? f.Wfact_t : nothing,
     paramjac = __has_paramjac(f) ? f.paramjac : nothing,
     syms = __has_syms(f) ? f.syms : nothing,
     indepsym = __has_indepsym(f) ? f.indepsym : nothing,
-    paramsyms = __has_paramsyms(f) ? f.paramsyms :
-                nothing,
-    observed = __has_observed(f) ? f.observed :
-               DEFAULT_OBSERVED,
+    paramsyms = __has_paramsyms(f) ? f.paramsyms : nothing,
+    observed = __has_observed(f) ? f.observed : DEFAULT_OBSERVED,
     colorvec = __has_colorvec(f) ? f.colorvec : nothing,
     bccolorvec = __has_colorvec(bc) ? bc.colorvec : nothing,
-    sys = __has_sys(f) ? f.sys : nothing) where {iip, specialize}
+    sys = __has_sys(f) ? f.sys : nothing) where {iip, specialize, twopoint}
     if mass_matrix === I && typeof(f) <: Tuple
         mass_matrix = ((I for i in 1:length(f))...,)
     end
@@ -3882,7 +3872,7 @@
         _bccolorvec = bccolorvec
     end
 
-    bciip = isinplace(bc, 4, "bc", iip)
+    bciip = !twopoint ? isinplace(bc, 4, "bc", iip) : isinplace(bc, 3, "bc", iip)
     jaciip = jac !== nothing ? isinplace(jac, 4, "jac", iip) : iip
     bcjaciip = bcjac !== nothing ? isinplace(bcjac, 4, "bcjac", bciip) : bciip
     tgradiip = tgrad !== nothing ? isinplace(tgrad, 4, "tgrad", iip) : iip
@@ -3892,66 +3882,62 @@
     Wfact_tiip = Wfact_t !== nothing ? isinplace(Wfact_t, 5, "Wfact_t", iip) : iip
     paramjaciip = paramjac !== nothing ? isinplace(paramjac, 4, "paramjac", iip) : iip
 
-    nonconforming = (jaciip,
-        tgradiip,
-        jvpiip,
-        vjpiip,
-        Wfactiip,
-        Wfact_tiip,
+    nonconforming = (bciip, jaciip, tgradiip, jvpiip, vjpiip, Wfactiip, Wfact_tiip,
         paramjaciip) .!= iip
     bc_nonconforming = bcjaciip .!= bciip
     if any(nonconforming)
         nonconforming = findall(nonconforming)
-        functions = ["jac", "bcjac", "tgrad", "jvp", "vjp", "Wfact", "Wfact_t", "paramjac"][nonconforming]
+        functions = ["bc", "jac", "bcjac", "tgrad", "jvp", "vjp", "Wfact", "Wfact_t",
+            "paramjac"][nonconforming]
         throw(NonconformingFunctionsError(functions))
     end
 
+    if twopoint
+        if iip && (bcresid_prototype === nothing || length(bcresid_prototype) != 2)
+            error("bcresid_prototype must be a tuple / indexable collection of length 2 for a inplace TwoPointBVPFunction")
+        end
+        if bcresid_prototype !== nothing && length(bcresid_prototype) == 2
+            bcresid_prototype = ArrayPartition(bcresid_prototype[1], bcresid_prototype[2])
+        end
+    end
+
     if any(bc_nonconforming)
         bc_nonconforming = findall(bc_nonconforming)
         functions = ["bcjac"][bc_nonconforming]
         throw(NonconformingFunctionsError(functions))
     end
 
     if specialize === NoSpecialize
-        BVPFunction{iip, specialize, Any, Any, Any, Any, Any,
-            Any, Any, Any, Any, Any, Any, Any, Any, Any,
+        BVPFunction{iip, specialize, twopoint, Any, Any, Any, Any, Any,
+            Any, Any, Any, Any, Any, Any, Any, Any, Any, Any,
             Any, typeof(syms), typeof(indepsym), typeof(paramsyms),
             Any, typeof(_colorvec), typeof(_bccolorvec), Any}(f, bc, mass_matrix,
-            analytic,
-            tgrad,
-            jac, bcjac, jvp, vjp,
-            jac_prototype,
-            bcjac_prototype,
-            sparsity, Wfact,
-            Wfact_t,
-            paramjac, syms,
-            indepsym, paramsyms,
-            observed,
+            analytic, tgrad, jac, bcjac, jvp, vjp, jac_prototype,
+            bcjac_prototype, bcresid_prototype,
+            sparsity, Wfact, Wfact_t, paramjac, syms, indepsym, paramsyms, observed,
             _colorvec, _bccolorvec, sys)
     else
-        BVPFunction{iip, specialize, typeof(f), typeof(bc), typeof(mass_matrix),
-            typeof(analytic),
-            typeof(tgrad),
-            typeof(jac), typeof(bcjac), typeof(jvp), typeof(vjp), typeof(jac_prototype),
-            typeof(bcjac_prototype),
-            typeof(sparsity), typeof(Wfact), typeof(Wfact_t),
-            typeof(paramjac), typeof(syms), typeof(indepsym), typeof(paramsyms),
-            typeof(observed),
+        BVPFunction{iip, specialize, twopoint, typeof(f), typeof(bc), typeof(mass_matrix),
+            typeof(analytic), typeof(tgrad), typeof(jac), typeof(bcjac), typeof(jvp),
+            typeof(vjp), typeof(jac_prototype),
+            typeof(bcjac_prototype), typeof(bcresid_prototype), typeof(sparsity),
+            typeof(Wfact), typeof(Wfact_t), typeof(paramjac), typeof(syms),
+            typeof(indepsym), typeof(paramsyms), typeof(observed),
             typeof(_colorvec), typeof(_bccolorvec), typeof(sys)}(f, bc, mass_matrix, analytic,
             tgrad, jac, bcjac, jvp, vjp,
-            jac_prototype, bcjac_prototype, sparsity,
+            jac_prototype, bcjac_prototype, bcresid_prototype, sparsity,
             Wfact, Wfact_t, paramjac,
             syms, indepsym, paramsyms, observed,
             _colorvec, _bccolorvec, sys)
     end
 end
 
-function BVPFunction{iip}(f, bc; kwargs...) where {iip}
-    BVPFunction{iip, FullSpecialize}(f, bc; kwargs...)
+function BVPFunction{iip}(f, bc; twopoint::Bool=false, kwargs...) where {iip}
+    BVPFunction{iip, FullSpecialize, twopoint}(f, bc; kwargs...)
 end
 BVPFunction{iip}(f::BVPFunction, bc; kwargs...) where {iip} = f
-function BVPFunction(f, bc; kwargs...)
-    BVPFunction{isinplace(f, 4), FullSpecialize}(f, bc; kwargs...)
+function BVPFunction(f, bc; twopoint::Bool=false, kwargs...)
+    BVPFunction{isinplace(f, 4), FullSpecialize, twopoint}(f, bc; kwargs...)
 end
 BVPFunction(f::BVPFunction; kwargs...) = f