Add a nlls trait to BVProblem

src/SciMLBase.jl

@@ -180,7 +180,7 @@ $(TYPEDEF)
 
 Base for types which define BVP problems.
 """
-abstract type AbstractBVProblem{uType, tType, isinplace} <:
+abstract type AbstractBVProblem{uType, tType, isinplace, nlls} <:
               AbstractODEProblem{uType, tType, isinplace} end
 
 """

src/problems/bvp_problems.jl

@@ -11,7 +11,7 @@
 @doc doc"""
 
 Defines an BVP problem.
-Documentation Page: https://docs.sciml.ai/DiffEqDocs/stable/types/bvp_types/
+Documentation Page: [https://docs.sciml.ai/DiffEqDocs/stable/types/bvp_types/](https://docs.sciml.ai/DiffEqDocs/stable/types/bvp_types/)
 
 ## Mathematical Specification of a BVP Problem
 
@@ -41,16 +41,16 @@
 ### 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,
+or if we have an initial guess function `initialGuess(p, 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` must be inplace if `f` is inplace. Otherwise it must be
@@ -104,9 +104,17 @@
 * `tspan`: The timespan for the problem.
 * `p`: The parameters for the problem. Defaults to `NullParameters`
 * `kwargs`: The keyword arguments passed onto the solves.
+
+### Special Keyword Arguments
+
+- `nlls`: Specify that the BVP is a nonlinear least squares problem. Use `Val(true)` or
+  `Val(false)` for type stability. By default this is automatically inferred based on the
+  size of the input and outputs, however this is type unstable for any array type that
+  doesn't store array size as part of type information. If we can't reliably infer this,
+  we set it to `Nothing`. Downstreams solvers must be setup to deal with this case.
 """
-struct BVProblem{uType, tType, isinplace, P, F, PT, K} <:
-       AbstractBVProblem{uType, tType, isinplace}
+struct BVProblem{uType, tType, isinplace, nlls, P, F, PT, K} <:
+       AbstractBVProblem{uType, tType, isinplace, nlls}
     f::F
     u0::uType
     tspan::tType
@@ -115,18 +123,56 @@
     kwargs::K
 
     @add_kwonly function BVProblem{iip}(f::AbstractBVPFunction{iip, TP}, u0, tspan,
-            p = NullParameters(); problem_type = nothing, kwargs...) where {iip, TP}
+            p = NullParameters(); problem_type = nothing, nlls = nothing,
+            kwargs...) where {iip, TP}
         _u0 = prepare_initial_state(u0)
         _tspan = promote_tspan(tspan)
         warn_paramtype(p)
         prob_type = TP ? TwoPointBVProblem{iip}() : StandardBVProblem()
+
         # Needed to ensure that `problem_type` doesn't get passed in kwargs
         if problem_type === nothing
             problem_type = prob_type
         else
             @assert prob_type===problem_type "This indicates incorrect problem type specification! Users should never pass in `problem_type` kwarg, this exists exclusively for internal use."
         end
-        return new{typeof(_u0), typeof(_tspan), iip, typeof(p), typeof(f),
+
+        if nlls === nothing
+            if !hasmethod(length, Tuple{typeof(_u0)})
+                # If _u0 is a function for initial guess we won't be able to infer
+                __u0 = _u0 isa Function ?
+                       (hasmethod(_u0, Tuple{typeof(p), typeof(first(_tspan))}) ?
+                        _u0(p, first(_tspan)) : _u0(first(_tspan))) : nothing
+            else
+                __u0 = _u0
+            end
+            # Try to infer it
+            if __u0 isa Nothing
+                _nlls = Nothing
+            elseif problem_type isa TwoPointBVProblem
+                if f.bcresid_prototype !== nothing
+                    l1, l2 = length(f.bcresid_prototype[1]), length(f.bcresid_prototype[2])
+                    _nlls = l1 + l2 != length(__u0)
+                else
+                    # iip without bcresid_prototype is not possible
+                    if !iip
+                        l1 = length(f.bc[1](u0, p))
+                        l2 = length(f.bc[2](u0, p))
+                        _nlls = l1 + l2 != length(__u0)
+                    end
+                end
+            else
+                if f.bcresid_prototype !== nothing
+                    _nlls = length(f.bcresid_prototype) != length(__u0)
+                else
+                    _nlls = Nothing # Cannot reliably infer
+                end
+            end
+        else
+            _nlls = _unwrap_val(nlls)
+        end
+
+        return new{typeof(_u0), typeof(_tspan), iip, _nlls, typeof(p), typeof(f),
             typeof(problem_type), typeof(kwargs)}(f, _u0, _tspan, p, problem_type, kwargs)
     end
 

src/remake.jl

@@ -45,7 +45,8 @@
     (prob.f isa ODEFunction) ? !isfunctionwrapper(prob.f.f) : true
 end
 
-function remake(prob::AbstractSciMLProblem; u0 = missing, p = missing, interpret_symbolicmap = true, kwargs...)
+function remake(prob::AbstractSciMLProblem; u0 = missing,
+        p = missing, interpret_symbolicmap = true, kwargs...)
     u0, p = updated_u0_p(prob, u0, p; interpret_symbolicmap)
     _remake_internal(prob; kwargs..., u0, p)
 end
@@ -54,7 +55,8 @@
     _remake_internal(prob; kwargs...)
 end
 
-function remake(prob::AbstractIntegralProblem; p = missing, interpret_symbolicmap = true, kwargs...)
+function remake(
+        prob::AbstractIntegralProblem; p = missing, interpret_symbolicmap = true, kwargs...)
     p = updated_p(prob, p; interpret_symbolicmap)
     _remake_internal(prob; kwargs..., p)
 end
@@ -128,16 +130,15 @@
 
 Remake the given `BVProblem`.
 """
-function remake(prob::BVProblem; f = missing, bc = missing, u0 = missing, tspan = missing,
-        p = missing, kwargs = missing, problem_type = missing, interpret_symbolicmap = true, _kwargs...)
+function remake(prob::BVProblem{uType, tType, iip, nlls}; f = missing, bc = missing,
+        u0 = missing, tspan = missing, p = missing, kwargs = missing, problem_type = missing,
+        interpret_symbolicmap = true, _kwargs...) where {uType, tType, iip, nlls}
     if tspan === missing
         tspan = prob.tspan
     end
 
     u0, p = updated_u0_p(prob, u0, p; interpret_symbolicmap)
 
-    iip = isinplace(prob)
-
     if problem_type === missing
         problem_type = prob.problem_type
     end
@@ -170,9 +171,11 @@
     end
 
     if kwargs === missing
-        BVProblem{iip}(_f, bc, u0, tspan, p; problem_type, prob.kwargs..., _kwargs...)
+        BVProblem{iip}(
+            _f, bc, u0, tspan, p; problem_type, nlls = Val(nlls), prob.kwargs...,
+            _kwargs...)
     else
-        BVProblem{iip}(_f, bc, u0, tspan, p; problem_type, kwargs...)
+        BVProblem{iip}(_f, bc, u0, tspan, p; problem_type, nlls = Val(nlls), kwargs...)
     end
 end
 
@@ -254,7 +257,6 @@
         kwargs = missing,
         interpret_symbolicmap = true,
         _kwargs...)
-
     u0, p = updated_u0_p(prob, u0, p; interpret_symbolicmap)
     if f === missing
         f = prob.f
@@ -393,10 +395,11 @@
     end
     if eltype(p) <: Pair
         if interpret_symbolicmap
-            has_sys(prob.f) || throw(ArgumentError("This problem does not support symbolic maps with " *
-                                "`remake`, i.e. it does not have a symbolic origin. Please use `remake`" *
-                                "with the `p` keyword argument as a vector of values (paying attention to" *
-                                "parameter order) or pass `interpret_symbolicmap = false` as a keyword argument"))
+            has_sys(prob.f) ||
+                throw(ArgumentError("This problem does not support symbolic maps with " *
+                                    "`remake`, i.e. it does not have a symbolic origin. Please use `remake`" *
+                                    "with the `p` keyword argument as a vector of values (paying attention to" *
+                                    "parameter order) or pass `interpret_symbolicmap = false` as a keyword argument"))
         else
             return p
         end

src/scimlfunctions.jl

@@ -1929,35 +1929,46 @@
 A representation of a BVP function `f`, defined by:
 
 ```math
-\frac{du}{dt}=f(u,p,t)
+\frac{du}{dt} = f(u, p, t)
 ```
 
 and the constraints:
 
 ```math
-\frac{du}{dt}=g(u,p,t)
+g(u, p, t) = 0
+```
+
+If the size of `g(u, p, t)` is different from the size of `u`, then the constraints are
+interpreted as a least squares problem, i.e. the objective function is:
+
+```math
+\min_{u} \| g_i(u, p, t) \|^2
 ```
 
 and all of its related functions, such as the Jacobian of `f`, its gradient
 with respect to time, and more. For all cases, `u0` is the initial condition,
 `p` are the parameters, and `t` is the independent variable.
 
 ```julia
-BVPFunction{iip,specialize}(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,
-                           paramjac = __has_paramjac(f) ? f.paramjac : nothing,
-                           colorvec = __has_colorvec(f) ? f.colorvec : nothing,
-                           bccolorvec = __has_colorvec(f) ? bc.colorvec : nothing,
-                           sys = __has_sys(f) ? f.sys : nothing)
+BVPFunction{iip, specialize}(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,
+    paramjac = __has_paramjac(f) ? f.paramjac : nothing,
+    syms = nothing,
+    indepsym= nothing,
+    paramsyms = nothing,
+    colorvec = __has_colorvec(f) ? f.colorvec : nothing,
+    bccolorvec = __has_colorvec(f) ? bc.colorvec : nothing,
+    sys = __has_sys(f) ? f.sys : nothing,
+    twopoint::Union{Val, Bool} = Val(false)
 ```
 
 Note that both the function `f` and boundary condition `bc` are required. `f` should
@@ -1985,7 +1996,7 @@
   sparsity patterns should use a `SparseMatrixCSC` with a correct sparsity pattern for the Jacobian.
   The default is `nothing`, which means a dense Jacobian.
 - `bcjac_prototype`: a prototype matrix matching the type that matches the Jacobian. For example,
- if the Jacobian is tridiagonal, then an appropriately sized `Tridiagonal` matrix can be used
+  if the Jacobian is tridiagonal, then an appropriately sized `Tridiagonal` matrix can be used
   as the prototype and integrators will specialize on this structure where possible. Non-structured
   sparsity patterns should use a `SparseMatrixCSC` with a correct sparsity pattern for the Jacobian.
   The default is `nothing`, which means a dense Jacobian.
@@ -2003,6 +2014,11 @@
   internally computed on demand when required. The cost of this operation is highly dependent
   on the sparsity pattern.
 
+Additional Options:
+
+- `twopoint`: Specify that the BVP is a two-point boundary value problem. Use `Val(true)` or
+  `Val(false)` for type stability.
+
 ## iip: In-Place vs Out-Of-Place
 
 For more details on this argument, see the ODEFunction documentation.
@@ -3801,7 +3817,7 @@
 
     _f = prepare_function(f)
 
-    sys = sys_or_symbolcache(sys, syms, paramsyms, indepsym)
+    sys = something(sys, SymbolCache(syms, paramsyms, indepsym))
 
     if specialize === NoSpecialize
         BVPFunction{iip, specialize, twopoint, Any, Any, Any, Any, Any,
@@ -3813,9 +3829,9 @@
             sparsity, Wfact, Wfact_t, paramjac, observed,
             _colorvec, _bccolorvec, sys)
     else
-        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),
+        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(observed),
             typeof(_colorvec), typeof(_bccolorvec), typeof(sys)}(
@@ -3897,7 +3913,9 @@
 function sys_or_symbolcache(sys, syms, paramsyms, indepsym = nothing)
     if sys === nothing &&
        (syms !== nothing || paramsyms !== nothing || indepsym !== nothing)
-        Base.depwarn("The use of keyword arguments `syms`, `paramsyms` and `indepsym` for `SciMLFunction`s is deprecated. Pass `sys = SymbolCache(syms, paramsyms, indepsym)` instead.", :syms)
+        Base.depwarn(
+            "The use of keyword arguments `syms`, `paramsyms` and `indepsym` for `SciMLFunction`s is deprecated. Pass `sys = SymbolCache(syms, paramsyms, indepsym)` instead.",
+            :syms)
         sys = SymbolCache(syms, paramsyms, indepsym)
     end
     return sys