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ChrisRackauckasChrisRackauckas
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Merge pull request #3224 from AayushSabharwal/as/parse-string
feat: add function to parse variable from string
2 parents dddcd2c + 2186298 commit 21dff0c

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‎docs/src/basics/FAQ.md

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@@ -82,6 +82,16 @@ parameter_index(sys, sym)
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Note that while the variable index will be an integer, the parameter index is a struct of
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type `ParameterIndex` whose internals should not be relied upon.
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## Can I index with strings?
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Strings are not considered symbolic variables, and thus cannot directly be used for symbolic
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indexing. However, ModelingToolkit does provide a method to parse the string representation of
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a variable, given the system in which that variable exists.
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```@docs
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ModelingToolkit.parse_variable
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```
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## Transforming value maps to arrays
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ModelingToolkit.jl allows (and recommends) input maps like `[x => 2.0, y => 3.0]`

‎src/systems/abstractsystem.jl

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@@ -3302,6 +3302,96 @@ function dump_unknowns(sys::AbstractSystem)
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end
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end
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"""
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$(TYPEDSIGNATURES)
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Return the variable in `sys` referred to by its string representation `str`.
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Roughly supports the following CFG:
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```
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varname = "D(" varname ")" | "Differential(" iv ")(" varname ")" | arrvar | maybe_dummy_var
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arrvar = maybe_dummy_var "[idxs...]"
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idxs = int | int "," idxs
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maybe_dummy_var = namespacedvar | namespacedvar "(" iv ")" |
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namespacedvar "(" iv ")" "ˍ" ts | namespacedvar "ˍ" ts |
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namespacedvar "ˍ" ts "(" iv ")"
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ts = iv | iv ts
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namespacedvar = ident "₊" namespacedvar | ident "." namespacedvar | ident
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```
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Where `iv` is the independent variable, `int` is an integer and `ident` is an identifier.
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"""
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function parse_variable(sys::AbstractSystem, str::AbstractString)
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iv = has_iv(sys) ? string(getname(get_iv(sys))) : nothing
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# I'd write a regex to validate `str`, but https://xkcd.com/1171/
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str = strip(str)
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derivative_level = 0
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while ((cond1 = startswith(str, "D(")) || startswith(str, "Differential(")) && endswith(str, ")")
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if cond1
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derivative_level += 1
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str = _string_view_inner(str, 2, 1)
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continue
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end
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_tmpstr = _string_view_inner(str, 13, 1)
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if !startswith(_tmpstr, "$iv)(")
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throw(ArgumentError("Expected differential with respect to independent variable $iv in $str"))
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end
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derivative_level += 1
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str = _string_view_inner(_tmpstr, length(iv) + 2, 0)
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end
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arr_idxs = nothing
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if endswith(str, ']')
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open_idx = only(findfirst('[', str))
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idxs_range = nextind(str, open_idx):prevind(str, lastindex(str))
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idxs_str = view(str, idxs_range)
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str = view(str, firstindex(str):prevind(str, open_idx))
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arr_idxs = map(Base.Fix1(parse, Int), eachsplit(idxs_str, ","))
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end
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if iv !== nothing && endswith(str, "($iv)")
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str = _string_view_inner(str, 0, 2 + length(iv))
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end
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dummyderivative_level = 0
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if iv !== nothing && (dd_idx = findfirst('ˍ', str)) !== nothing
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t_idx = findnext(iv, str, dd_idx)
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while t_idx !== nothing
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dummyderivative_level += 1
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t_idx = findnext(iv, str, nextind(str, last(t_idx)))
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end
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str = view(str, firstindex(str):prevind(str, dd_idx))
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end
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if iv !== nothing && endswith(str, "($iv)")
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str = _string_view_inner(str, 0, 2 + length(iv))
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end
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cur = sys
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for ident in eachsplit(str, ('.', NAMESPACE_SEPARATOR))
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ident = Symbol(ident)
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hasproperty(cur, ident) ||
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throw(ArgumentError("System $(nameof(cur)) does not have a subsystem/variable named $(ident)"))
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cur = getproperty(cur, ident)
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end
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if arr_idxs !== nothing
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cur = cur[arr_idxs...]
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end
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for i in 1:(derivative_level + dummyderivative_level)
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cur = Differential(get_iv(sys))(cur)
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end
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return cur
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end
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function _string_view_inner(str, startoffset, endoffset)
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view(str,
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nextind(str, firstindex(str), startoffset):prevind(str, lastindex(str), endoffset))
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end
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### Functions for accessing algebraic/differential equations in systems ###
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"""

‎test/variable_utils.jl

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using ModelingToolkit, Test
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using ModelingToolkit: value, vars
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using ModelingToolkit: value, vars, parse_variable
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using SymbolicUtils: <ₑ
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@parameters α β δ
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expr = (((1 / β - 1) + δ) / α)^(1 / (α - 1))
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ref = sort([β, δ, α], lt = <ₑ)
@@ -41,3 +42,106 @@ ts = collect_ivs([eq])
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res = vars(fn([x, y], z))
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@test length(res) == 3
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end
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@testset "parse_variable with iv: $iv" for iv in [t, only(@independent_variables tt)]
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D = Differential(iv)
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function Lorenz(; name)
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@variables begin
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x(iv)
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y(iv)
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z(iv)
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end
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@parameters begin
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σ
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ρ
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β
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end
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sys = ODESystem(
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[D(D(x)) ~ σ * (y - x)
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D(y) ~ x * (ρ - z) - y
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D(z) ~ x * y - β * z], iv; name)
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end
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function ArrSys(; name)
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@variables begin
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x(iv)[1:2]
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end
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@parameters begin
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p[1:2, 1:2]
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end
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sys = ODESystem([D(D(x)) ~ p * x], iv; name)
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end
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function Outer(; name)
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@named 😄 = Lorenz()
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@named arr = ArrSys()
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sys = ODESystem(Equation[], iv; name, systems = [😄, arr])
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end
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@mtkbuild sys = Outer()
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for (str, var) in [
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# unicode system, scalar variable
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("😄.x", sys.😄.x),
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("😄.x($iv)", sys.😄.x),
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("😄₊x", sys.😄.x),
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("😄₊x($iv)", sys.😄.x),
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# derivative
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("D(😄.x)", D(sys.😄.x)),
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("D(😄.x($iv))", D(sys.😄.x)),
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("D(😄₊x)", D(sys.😄.x)),
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("D(😄₊x($iv))", D(sys.😄.x)),
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("Differential($iv)(😄.x)", D(sys.😄.x)),
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("Differential($iv)(😄.x($iv))", D(sys.😄.x)),
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("Differential($iv)(😄₊x)", D(sys.😄.x)),
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("Differential($iv)(😄₊x($iv))", D(sys.😄.x)),
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# other derivative
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("😄.xˍ$iv", D(sys.😄.x)),
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("😄.x($iv)ˍ$iv", D(sys.😄.x)),
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("😄₊xˍ$iv", D(sys.😄.x)),
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("😄₊x($iv)ˍ$iv", D(sys.😄.x)),
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# scalar parameter
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("😄.σ", sys.😄.σ),
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("😄₊σ", sys.😄.σ),
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# array variable
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("arr.x", sys.arr.x),
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("arr₊x", sys.arr.x),
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("arr.x($iv)", sys.arr.x),
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("arr₊x($iv)", sys.arr.x),
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# getindex
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("arr.x[1]", sys.arr.x[1]),
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("arr₊x[1]", sys.arr.x[1]),
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("arr.x($iv)[1]", sys.arr.x[1]),
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("arr₊x($iv)[1]", sys.arr.x[1]),
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# derivative
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("D(arr.x($iv))", D(sys.arr.x)),
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("D(arr₊x($iv))", D(sys.arr.x)),
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("D(arr.x[1])", D(sys.arr.x[1])),
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("D(arr₊x[1])", D(sys.arr.x[1])),
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("D(arr.x($iv)[1])", D(sys.arr.x[1])),
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("D(arr₊x($iv)[1])", D(sys.arr.x[1])),
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("Differential($iv)(arr.x($iv))", D(sys.arr.x)),
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("Differential($iv)(arr₊x($iv))", D(sys.arr.x)),
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("Differential($iv)(arr.x[1])", D(sys.arr.x[1])),
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("Differential($iv)(arr₊x[1])", D(sys.arr.x[1])),
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("Differential($iv)(arr.x($iv)[1])", D(sys.arr.x[1])),
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("Differential($iv)(arr₊x($iv)[1])", D(sys.arr.x[1])),
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# other derivative
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("arr.xˍ$iv", D(sys.arr.x)),
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("arr₊xˍ$iv", D(sys.arr.x)),
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("arr.xˍ$iv($iv)", D(sys.arr.x)),
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("arr₊xˍ$iv($iv)", D(sys.arr.x)),
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("arr.xˍ$iv[1]", D(sys.arr.x[1])),
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("arr₊xˍ$iv[1]", D(sys.arr.x[1])),
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("arr.xˍ$iv($iv)[1]", D(sys.arr.x[1])),
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("arr₊xˍ$iv($iv)[1]", D(sys.arr.x[1])),
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("arr.x($iv)ˍ$iv", D(sys.arr.x)),
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("arr₊x($iv)ˍ$iv", D(sys.arr.x)),
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("arr.x($iv)ˍ$iv[1]", D(sys.arr.x[1])),
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("arr₊x($iv)ˍ$iv[1]", D(sys.arr.x[1])),
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# array parameter
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("arr.p", sys.arr.p),
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("arr₊p", sys.arr.p),
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("arr.p[1, 2]", sys.arr.p[1, 2]),
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("arr₊p[1, 2]", sys.arr.p[1, 2])
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]
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@test isequal(parse_variable(sys, str), var)
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end
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end

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