Skip to content

Latest commit

 

History

History
52 lines (46 loc) · 3.76 KB

NEWS.md

File metadata and controls

52 lines (46 loc) · 3.76 KB

ModelingToolkit v9 Release Notes

Upgrade guide

  • The function states is renamed to unknowns. In a similar vein:

    • unknown_states is now solved_unknowns.
    • get_states is get_unknowns.
    • get_unknown_states is now get_solved_unknowns.

  • The default backend for using units in models is now DynamicQuantities.jl instead of Unitful.jl.

  • ModelingToolkit.jl now exports common definitions of t (time independent variable) and D (the first derivative with respect to t). Any models made using ModelingToolkit.jl should leverage these common definitions. There are three variants:

    • t and D use DynamicQuantities.jl units. This is the default for standard library components.
    • t_unitful and D_unitful use Unitful.jl units.
    • t_nounits and D_nounits are unitless.

  • ODAEProblem is deprecated in favor of ODEProblem.

  • Specifying the independent variable for an ODESystem is now mandatory. The ODESystem(eqs) constructor is removed. Use ODESystem(eqs,t) instead.

  • Systems must be marked as complete before creating *Function/*FunctionExpr/*Problem/ *ProblemExpr. Typically this involved using @mtkbuild to create the system or calling structural_simplify on an existing system.

  • All systems will perform parameter splitting by default. Problems created using ModelingToolkit.jl systems will have a custom struct instead of a Vector of parameters. The internals of this type are undocumented and subject to change without notice or a breaking release. Parameter values can be queried, updated or manipulated using SciMLStructures.jl or SymbolicIndexingInterface.jl. This also requires that the symbolic type of a parameter match its assigned value. For example, @parameters p will always use a Float64 value for p. To use Int instead, use @parameters p::Int. Array-valued parameters must be array symbolics; @parameters p = [1.0, 2.0] is now invalid and must be changed to @parameters p[1:2] = [1.0, 2.0]. The index of a parameter in the system is also not guaranteed to be an Int, and will instead be a custom undocumented type. Parameters that have a default value depending on other parameters are now treated as dependent parameters. Their value cannot be modified directly. Whenever a parameter value is changed, dependent parameter values are recalculated. For example, if @parameters p1 p2 = 3p1 then p2 can not be modified directly. If p1 is changed, then p2 will be updated accordingly. To restore the old behavior:

    • Pass the split = false keyword to structural_simplify. E.g. ss = structural_simplify(sys; split = false).
    • Pass split = false to @mtkbuild. E.g. @mtkbuild sys = ODESystem(...) split = false.

  • Discrete-time system using Difference are unsupported. Instead, use the new Clock-based syntax.

  • Automatic scalarization has been removed, meaning that vector variables need to be treated with proper vector equations. For example, [p[1] => 1.0, p[2] => 2.0] is no longer allowed in default equations, use [p => [1.0, 2.0]] instead. Also, array equations like for @variables u[1:2] have D(u) ~ A*u as an array equation. If the scalarized version is desired, use scalarize(u).

  • Parameter dependencies are now supported. They can be specified using the syntax (single_parameter => expression_involving_other_parameters) and a Vector of these can be passed to the parameter_dependencies keyword argument of ODESystem, SDESystem and JumpSystem. The dependent parameters are updated whenever other parameters are modified, e.g. in callbacks.

  • Support for IfElse.jl has been dropped. Base.ifelse can be used instead.