Automatically move differentials to the left side #1164
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Co-authored-by: Yingbo Ma <mayingbo5@gmail.com>
src/systems/diffeqs/odesystem.jl
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| function move_diffs(eq::Equation,r) | ||
| # Do not modify `D(x) ~ ...`, already correct | ||
| # Ignore `δ(x) ~ ...` for now | ||
| if !(eq.lhs isa Term && ModelingToolkit.operation(eq.lhs) isa Differential) && |
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This code already lives in MTK.
| 0 ~ y-x] | ||
| @test isequal(eqs2,eqs3) | ||
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| eqs = [0 ~ x + y + D(x) |
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What happens if there's D(x)/x ~ x or D(x)*x ~ x?
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D(x)/x ~ x will be untouched like before. D(x)*x ~ x will give you -D(x)*x ~ -x, which is a little odd but works fine for DAEProblem.
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Could you test these cases as well? Also sin(D(x) * x) ~ x, sin(D(x) + x) ~ x, sin(D(x))*x ~ x, D(x)*D(y), etc.
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@YingboMa one last test now throws the wrong error. It errored before, but it shouldn't throw this error. julia> equations(sys)
3-element Vector{Equation}:
0 ~ x(t) + sin(u1(t) + u2(t))
Differential(t)(x(t)) ~ x(t) + y1(t)
0 ~ sin(y2(t)) - cos(x(t))
fullvars = Any[Differential(t)(x(t)), x(t), u1(t), u2(t), y2(t)]How come |
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Maybe rules drop the metadata. |
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What's the MWE? |
# Example 5 from Pantelides' original paper
@parameters t
params = collect(@parameters y1(t) y2(t))
sts = collect(@variables x(t) u1(t) u2(t))
D = Differential(t)
eqs = [
0 ~ x + sin(u1 + u2)
D(x) ~ x + y1
cos(x) ~ sin(y2)
]
@named sys = ODESystem(eqs, t, sts, params)
@test_throws ModelingToolkit.InvalidSystemException structural_simplify(sys) |
Fixes #860