diff --git a/docs/src/basics/MTKModel_Connector.md b/docs/src/basics/MTKModel_Connector.md new file mode 100644 index 0000000000..7fdcbf4db9 --- /dev/null +++ b/docs/src/basics/MTKModel_Connector.md @@ -0,0 +1,156 @@ +## Defining components with `@mtkmodel` + +`@mtkmodel` is a convenience macro to define ModelingToolkit components. It returns `ModelingToolkit.Model`, which includes a constructor that returns an ODESystem, a `structure` dictionary with metadata and flag `isconnector` which is set to `false`. + +### What can an MTK-Model definition have? + +`@mtkmodel` definition contains begin blocks of + + - `@components`: for listing sub-components of the system + - `@equations`: for the list of equations + - `@extend`: for extending a base system and unpacking its states + - `@parameters`: for specifying the symbolic parameters + - `@structural_parameters`: for specifying non-symbolic parameters + - `@variables`: for specifing the states + +Let's explore these in more detail with the following example: + +```@example mtkmodel-example +using ModelingToolkit + +@mtkmodel ModelA begin + @parameters begin + k1 + k2 + end +end + +@mtkmodel ModelB begin + @parameters begin + p1 = 1.0, [description = "Parameter of ModelB"] + p2 = 1.0, [description = "Parameter of ModelB"] + end +end + +@mtkmodel ModelC begin + @structural_parameters begin + f = sin + end + begin + v_var = 1.0 + end + @variables begin + v(t) = v_var + end + @extend p1, p2 = model_b = ModelB(; p1) + @components begin + model_a = ModelA(; k1) + end + @equations begin + model_a.k1 ~ f(v) + end +end +``` + +#### `@parameters` and `@variables` begin block + + - Parameters and variables are declared with respective begin blocks. + - Variables must be functions of an independent variable. + - Optionally, default values and metadata can be specified for these parameters and variables. See `ModelB` in the above example. + - Along with creating parameters and variables, keyword arguments of same name with default value `nothing` are created. + - Whenever a parameter or variable has default value, for example `v(t) = 0.0`, a symbolic variable named `v` with default value 0.0 and a keyword argument `v`, with default value `nothing` are created.
This way, users can optionally pass new value of `v` while creating a component. + +```julia +julia > @named model_c = ModelC(; v = 2.0); + +julia > ModelingToolkit.getdefault(model_c.v) +2.0 +``` + +#### `@structural_parameters` begin block + + - This block is for non symbolic input arguements. These are for inputs that usually are not meant to be part of components; but influence how they are defined. One can list inputs like boolean flags, functions etc... here. + - Whenever default values are specified, unlike parameters/variables, they are reflected in the keyword argument list. + +#### `@extend` block + +To extend a partial system, + + - List the variables to unpack. If there is a single variable, explicitly specify it as a tuple. + - Give a name to the base system + - List the kwargs of the base system that should be listed as kwargs of the main component. + - Note that in above example, `p1` is promoted as an argument of `ModelC`. Users can set the value of `p1` as + +```julia +julia> @named model_c = ModelC(; p1 = 2.0) + +``` + +However, as `p2` isn't listed in the model definition, its default can't be modified by users. + +#### `@components` begin block + + - Declare the subcomponents within `@components` begin block. + - The arguments in these subcomponents are promoted as keyword arguments as `subcomponent_name__argname` with `nothing` as default value. + - Whenever components are created with `@named` macro, these can be accessed with `.` operator as `subcomponent_name.argname` + - In the above example, `k1` of `model_a` can be set in following ways: + +```julia +julia> @named model_c1 = ModelC(; model_a.k1 = 1); +# or as + +julia> model_c2 = ModelC(; name = :model_c, model_a__k1 = 1); + +``` + +And as `k2` isn't listed in the sub-component definition of `ModelC`, its default value can't be modified by users. + +#### `@equations` begin block + + - List all the equations here + +#### A begin block + + - Any other Julia operations can be included with dedicated begin blocks. + +## Defining connectors with `@connector` + +`@connector` returns `ModelingToolkit.Model`. It includes a constructor that returns a connector ODESystem, a `structure` dictionary with metadata and flag `isconnector` which is set to `true`. + +A simple connector can be defined with syntax similar to following example: + +```julia +using ModelingToolkit + +@connector Pin begin + v(t) = 0.0, [description = "Voltage"] + i(t), [connect = Flow] +end +``` + + - Variables (as function of independent variable) are listed out in the definition. These variables can optionally have default values and metadata like `descrption`, `connect` and so on. + +`@connector`s accepts begin blocks of `@components`, `@equations`, `@extend`, `@parameters`, `@structural_parameters`, `@variables`. These keywords mean the same as described above for `@mtkmodel`. + +!!! note + + For more examples of usage, checkout [ModelingToolkitStandardLibrary.jl](https://github.com/SciML/ModelingToolkitStandardLibrary.jl/) + +* * * + +### What's a `structure` dictionary? + +For components defined with `@mtkmodel` or `@connector`, a dictionary with metadata is created. It lists `:components` (sub-component list), `:extend` (the extended states and base system), `:parameters`, `:variables`, ``:kwargs`` (list of keyword arguments), `:independent_variable`, `:equations`. + +For example, the structure of `ModelC` is: + +```julia +julia> ModelC.structure +Dict{Symbol, Any} with 6 entries: + :components => [[:model_a, :ModelA]] + :variables => Dict{Symbol, Dict{Symbol, Any}}(:v=>Dict(:default=>:v_var)) + :kwargs => Dict{Symbol, Any}(:f=>:sin, :v=>:v_var, :p1=>nothing, :model_a__k1=>nothing) + :independent_variable => t + :extend => Any[[:p1, :p2], :model_b, :ModelB] + :equations => ["model_a.k1 ~ f(v)"] +``` diff --git a/src/systems/model_parsing.jl b/src/systems/model_parsing.jl index 6c73dfa743..6a95a6e9e8 100644 --- a/src/systems/model_parsing.jl +++ b/src/systems/model_parsing.jl @@ -1,6 +1,25 @@ +""" +$(TYPEDEF) + +ModelingToolkit component or connector with metadata + +# Fields +$(FIELDS) +""" struct Model{F, S} + """The constructor that returns ODESystem.""" f::F + """ + The dictionary with metadata like keyword arguements (:kwargs), base + system this Model extends (:extend), sub-components of the Model (:components), + variables (:variables), parameters (:parameters), structural parameters + (:structural_parameters) and equations (:equations). + """ structure::S + """ + This flag is `true` when the Model is a connector and is `false` when it is + a component + """ isconnector::Bool end (m::Model)(args...; kw...) = m.f(args...; kw...)