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Adding inputs and outputs functions #1209

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d07d063
Adding inputs and outputs functions
dannys4 Aug 17, 2021
b6ed591
export functions
dannys4 Aug 17, 2021
8b9df93
Adding documentation
dannys4 Aug 17, 2021
83be3de
Add observed to outputs
dannys4 Aug 17, 2021
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16 changes: 15 additions & 1 deletion src/ModelingToolkit.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,20 @@ function states end
"""
$(TYPEDSIGNATURES)

Get the set of states decorated as inputs for the given system.
"""
function inputs end

"""
$(TYPEDSIGNATURES)

Get the set of states decorated as outputs for the given system.
"""
function outputs end

"""
$(TYPEDSIGNATURES)

Get the set of parameters variables for the given system.
"""
function parameters end
Expand Down Expand Up @@ -173,7 +187,7 @@ export Differential, expand_derivatives, @derivatives
export Equation, ConstrainedEquation
export Term, Sym
export SymScope, LocalScope, ParentScope, GlobalScope
export independent_variables, independent_variable, states, parameters, equations, controls, observed, structure
export independent_variables, independent_variable, states, parameters, equations, controls, observed, structure, inputs, outputs
export structural_simplify
export DiscreteSystem, DiscreteProblem

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8 changes: 8 additions & 0 deletions src/systems/abstractsystem.jl
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Expand Up @@ -392,6 +392,14 @@ function states(sys::AbstractSystem)
[sts; reduce(vcat,namespace_variables.(systems))])
end

function inputs(sys::AbstractSystem)
[st for st in states(sys) if isinput(st)]
end

function outputs(sys::AbstractSystem)
[st for st in states(sys) if isoutput(st)]
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This may not be true. Do you want it to be true?

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@dannys4 dannys4 Aug 17, 2021 •
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In what case would it operate incorrectly?

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yeah they could be eliminated to observed?

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ah, so should I cat any states in observed that are also decorated as outputs?

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But then, you cannot calculate the Jacobian.

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@YingboMa YingboMa Aug 18, 2021 •
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Suppose we have the reduced output as an observed variable x ~ a + b with the equation D(y) ~ a + sin(a) + b. What's the derivative of the right hand wrt x ~ a + b? We cannot differentiate this thing. First, matching a+b is hard. Second, we don't know if this a + b is from x. It could very well be something else.

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I disagree with you on the idea that the a+b needs to be "from" x, but I see your point nonetheless. Does that have anything to do with it being an output though? Your argument seems to be valid regardless of that. Right now, don't we just expect people to, for lack of better words, "not do that"?

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Given x is an output, what's the output Jacobian of

D(y) ~ a + b + x
0 ~ a + b - x

and what's the output Jacobian of

```julia
D(y) ~ 2a + 2b

wrt a+b?

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Say x isn't an output though. Isn't this still a problem? I'm failing to see where it being labelled as output=true comes in

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When linearizing control problems, we need to compute the Jacobian wrt the inputs or the outputs.

end

function parameters(sys::AbstractSystem)
ps = get_ps(sys)
systems = get_systems(sys)
Expand Down