SciMLSolutions

Definition of the AbstractSciMLSolution Interface

All AbstractSciMLSolution types are a subset of some AbstractArray. Types with time series (like ODESolution) are subtypes of RecursiveArrayTools.AbstractVectorOfArray and RecursiveArrayTools.AbstractDiffEqArray where appropriate. Types without a time series (like OptimizationSolution) are directly subsets of AbstractArray.

Array Interface

Instead of working on the Vector{uType} directly, we can use the provided array interface.

sol[j]

to access the value at timestep j (if the timeseries was saved), and

sol.t[j]

to access the value of t at timestep j. For multi-dimensional systems, this will address first by component and lastly by time, and thus

sol[i, j]

will be the ith component at timestep j. Hence, sol[j][i] == sol[i, j]. This is done because Julia is column-major, so the leading dimension should be contiguous in memory. If the independent variables had shape (for example, was a matrix), then i is the linear index. We can also access solutions with shape:

sol[i, k, j]

gives the [i,k] component of the system at timestep j. The colon operator is supported, meaning that

sol[i, :]

gives the timeseries for the ith component.

Common Field Names

u: the solution values
t: the independent variable values, matching the length of the solution, if applicable
resid: the residual of the solution, if applicable
original: the solution object from the original solver, if it's a wrapper algorithm
retcode: see the documentation section on return codes
prob: the problem that was solved
alg: the algorithm used to solve the problem

Return Codes (RetCodes)

The solution types have a retcode field which returns a SciMLBase.ReturnCode.T (from EnumX.jl, see that package for the semantics of handling EnumX types) signifying the error or satisfaction state of the solution.

SciMLBase.ReturnCode — Module

SciML.ReturnCode

SciML.ReturnCode is the standard return code enum interface for the SciML interface. Return codes are notes given by the solvers to indicate the state of the solution, for example whether it successfully solved the equations, whether it failed to solve the equations, and importantly, why it exited.

Using SciML.ReturnCode

SciML.ReturnCode use the interface of EnumX.jl and thus inherits all of the behaviors of being an EnumX. This includes the Enum type itself being referred to as SciML.ReturnCode.T, and each of the constituent enum states being referred to via getproperty, i.e. SciML.ReturnCode.Success.

Note About Success Checking

Previous iterations of the interface suggested using sol.retcode == :Success, however, that is now not advised instead should be replaced with SciMLBase.successful_retcode(sol). The reason is that there are many different codes that can be interpreted as successful, such as ReturnCode.Terminated which means successfully used terminate!(integrator) to end an integration at a user-specified condition. As such, successful_retcode is the most general way to query for if the solver did not error.

Properties

successful_retcode(retcode::ReturnCode.T): Determines whether the output enum is considered a success state of the solver, i.e. the solver successfully solved the equations. ReturnCode.Success is the most basic form, simply declaring that it was successful, but many more informative success return codes exist as well.