Merge pull request #2499 from ven-k/vkb/constant-in-mtkmodel

Parse constants in `@mtkmodel`

Author: ChrisRackauckas

docs/src/basics/ContextualVariables.md

@@ -20,7 +20,7 @@ All modeling projects have some form of parameters. `@parameters` marks a variab
 as being the parameter of some system, which allows automatic detection algorithms
 to ignore such variables when attempting to find the unknowns of a system.
 
-## Constants
+## [Constants](@id constants)
 
 Constants, defined by e.g. `@constants myconst1` are like parameters that:
 

docs/src/basics/MTKModel_Connector.md

@@ -24,6 +24,7 @@ equations.
 `@mtkmodel` definition contains begin blocks of
 
   - `@components`: for listing sub-components of the system
+  - `@constants`: for declaring constants
   - `@equations`: for the list of equations
   - `@extend`: for extending a base system and unpacking its unknowns
   - `@icon` : for embedding the model icon
@@ -52,6 +53,9 @@ end
 
 @mtkmodel ModelC begin
     @icon "https://github.com/SciML/SciMLDocs/blob/main/docs/src/assets/logo.png"
+    @constants begin
+        c::Int = 1, [description = "Example constant."]
+    end
     @structural_parameters begin
         f = sin
     end
@@ -107,6 +111,12 @@ end
   - This block is for non symbolic input arguments. 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.
 
+#### `@constants` begin block
+
+  - Declare constants in the model definition.
+  - The values of these can't be changed by the user.
+  - This works similar to symbolic constants described [here](@ref constants)
+
 #### `@parameters` and `@variables` begin block
 
   - Parameters and variables are declared with respective begin blocks.
@@ -220,7 +230,8 @@ end
 
 `structure` stores metadata that describes composition of a model. It includes:
 
-  - `:components`: List of sub-components in the form of [[name, sub_component_name],...].
+  - `:components`: The list of sub-components in the form of [[name, sub_component_name],...].
+  - `:constants`: Dictionary of constants mapped to its metadata.
   - `:extend`: The list of extended unknowns, name given to the base system, and name of the base system.
   - `:structural_parameters`: Dictionary of structural parameters mapped to their metadata.
   - `:parameters`: Dictionary of symbolic parameters mapped to their metadata. For
@@ -239,6 +250,7 @@ Dict{Symbol, Any} with 9 entries:
   :components            => Any[Union{Expr, Symbol}[:model_a, :ModelA]]
   :variables             => Dict{Symbol, Dict{Symbol, Any}}(:v=>Dict(:default=>:v_var, :type=>Real), :v_array=>Dict(:type=>Real, :size=>(2, 3)))
   :icon                  => URI("https://github.com/SciML/SciMLDocs/blob/main/docs/src/assets/logo.png")
+  :constants             => Dict{Symbol, Dict}(:c=>Dict{Symbol, Any}(:value=>1, :type=>Int64, :description=>"Example constant."))
   :kwargs                => Dict{Symbol, Dict}(:f=>Dict(:value=>:sin), :v=>Dict{Symbol, Union{Nothing, Symbol}}(:value=>:v_var, :type=>Real), :v_array=>Dict(:value=>nothing, :type=>Real), :p1=>Dict(:value=>nothing))
   :structural_parameters => Dict{Symbol, Dict}(:f=>Dict(:value=>:sin))
   :independent_variable  => t

src/systems/model_parsing.jl

@@ -36,6 +36,7 @@ end
 function _model_macro(mod, name, expr, isconnector)
     exprs = Expr(:block)
     dict = Dict{Symbol, Any}(
+        :constants => Dict{Symbol, Dict}(),
         :kwargs => Dict{Symbol, Dict}(),
         :structural_parameters => Dict{Symbol, Dict}()
     )
@@ -347,6 +348,8 @@ function parse_model!(exprs, comps, ext, eqs, icon, vs, ps, sps,
         parse_structural_parameters!(exprs, sps, dict, mod, body, kwargs)
     elseif mname == Symbol("@equations")
         parse_equations!(exprs, eqs, dict, body)
+    elseif mname == Symbol("@constants")
+        parse_constants!(exprs, dict, body, mod)
     elseif mname == Symbol("@icon")
         isassigned(icon) && error("This model has more than one icon.")
         parse_icon!(body, dict, icon, mod)
@@ -355,13 +358,53 @@ function parse_model!(exprs, comps, ext, eqs, icon, vs, ps, sps,
     end
 end
 
+function parse_constants!(exprs, dict, body, mod)
+    Base.remove_linenums!(body)
+    for arg in body.args
+        MLStyle.@match arg begin
+            Expr(:(=), Expr(:(::), a, type), Expr(:tuple, b, metadata)) || Expr(:(=), Expr(:(::), a, type), b) => begin
+                type = getfield(mod, type)
+                b = _type_check!(get_var(mod, b), a, type, :constants)
+                constant = first(@constants $a::type = b)
+                push!(exprs, :($a = $constant))
+                dict[:constants][a] = Dict(:value => b, :type => type)
+                if @isdefined metadata
+                    for data in metadata.args
+                        dict[:constants][a][data.args[1]] = data.args[2]
+                    end
+                end
+            end
+            Expr(:(=), a, Expr(:tuple, b, metadata)) => begin
+                constant = first(@constants $a = b)
+                push!(exprs, :($a = $constant))
+                dict[:constants][a] = Dict{Symbol, Any}(:value => get_var(mod, b))
+                for data in metadata.args
+                    dict[:constants][a][data.args[1]] = data.args[2]
+                end
+            end
+            Expr(:(=), a, b) => begin
+                constant = first(@constants $a = b)
+                push!(exprs, :($a = $constant))
+                dict[:constants][a] = Dict(:value => get_var(mod, b))
+            end
+            _ => error("""Malformed constant definition `$arg`. Please use the following syntax:
+                ```
+                @constants begin
+                    var = value, [description = "This is an example constant."]
+                end
+                ```
+            """)
+        end
+    end
+end
+
 function parse_structural_parameters!(exprs, sps, dict, mod, body, kwargs)
     Base.remove_linenums!(body)
     for arg in body.args
         MLStyle.@match arg begin
             Expr(:(=), Expr(:(::), a, type), b) => begin
-                type = Core.eval(mod, type)
-                b = _type_check!(Core.eval(mod, b), a, type, :structural_parameters)
+                type = getfield(mod, type)
+                b = _type_check!(get_var(mod, b), a, type, :structural_parameters)
                 push!(sps, a)
                 push!(kwargs, Expr(:kw, Expr(:(::), a, type), b))
                 dict[:structural_parameters][a] = dict[:kwargs][a] = Dict(
@@ -922,16 +965,15 @@ function parse_conditional_model_statements(comps, dict, eqs, exprs, kwargs, mod
         end))
 end
 
-function _type_check!(val, a, type, varclass)
+function _type_check!(val, a, type, class)
     if val isa type
         return val
     else
         try
             return convert(type, val)
-        catch
-            (e)
+        catch e
             throw(TypeError(Symbol("`@mtkmodel`"),
-                "`$varclass`, while assigning to `$a`", type, typeof(val)))
+                "`$class`, while assigning to `$a`", type, typeof(val)))
         end
     end
 end

test/model_parsing.jl

@@ -180,6 +180,23 @@ resistor = getproperty(rc, :resistor; namespace = false)
 
 @test length(equations(rc)) == 1
 
+@testset "Constants" begin
+    @mtkmodel PiModel begin
+        @constants begin
+            _p::Irrational = π, [description = "Value of Pi."]
+        end
+        @parameters begin
+            p = _p, [description = "Assign constant `_p` value."]
+        end
+    end
+
+    @named pi_model = PiModel()
+
+    @test typeof(ModelingToolkit.getdefault(pi_model.p)) <:
+          SymbolicUtils.BasicSymbolic{Irrational}
+    @test getdefault(getdefault(pi_model.p)) == π
+end
+
 @testset "Parameters and Structural parameters in various modes" begin
     @mtkmodel MockModel begin
         @parameters begin
@@ -400,14 +417,19 @@ end
 module PrecompilationTest
 push!(LOAD_PATH, joinpath(@__DIR__, "precompile_test"))
 using Unitful, Test, ModelParsingPrecompile, ModelingToolkit
+using ModelingToolkit: getdefault, scalarize
 @testset "Precompile packages with MTKModels" begin
     using ModelParsingPrecompile: ModelWithComponentArray
 
     @named model_with_component_array = ModelWithComponentArray()
 
-    @test ModelWithComponentArray.structure[:parameters][:R][:unit] == u"Ω"
+    @test ModelWithComponentArray.structure[:parameters][:r][:unit] == u"Ω"
     @test lastindex(parameters(model_with_component_array)) == 3
 
+    # Test the constant `k`. Manually k's value should be kept in sync here
+    # and the ModelParsingPrecompile.
+    @test all(getdefault.(getdefault.(scalarize(model_with_component_array.r))) .== 1)
+
     pop!(LOAD_PATH)
 end
 end

test/precompile_test/ModelParsingPrecompile.jl

@@ -3,8 +3,11 @@ module ModelParsingPrecompile
 using ModelingToolkit, Unitful
 
 @mtkmodel ModelWithComponentArray begin
+    @constants begin
+        k = 1, [description = "Default val of R"]
+    end
     @parameters begin
-        R(t)[1:3] = 1, [description = "Parameter array", unit = u"Ω"]
+        r(t)[1:3] = k, [description = "Parameter array", unit = u"Ω"]
     end
 end