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Check that equations contain at least one variable #2865

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be2f38d
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hersle Jul 16, 2024
544896d
Just error if an equation only contains parameters (and no variables)
hersle Jul 16, 2024
0453e72
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hersle Jul 16, 2024
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6 changes: 6 additions & 0 deletions src/utils.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -201,6 +201,12 @@ function check_equations(eqs, iv)
isequal(single_iv, iv) ||
throw(ArgumentError("Differential w.r.t. variable ($single_iv) other than the independent variable ($iv) are not allowed."))
end

for eq in eqs
vars, pars = collect_vars(eq, iv)
isempty(vars) && !isempty(pars) &&
throw(ArgumentError("Equation $eq contains only parameters, but relationships between parameters should be specified with defaults or parameter_dependencies."))
end
end
"""
Get all the independent variables with respect to which differentials are taken.
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6 changes: 6 additions & 0 deletions test/odesystem.jl
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Expand Up @@ -422,6 +422,12 @@ eqs = [
]
@test_throws ArgumentError ModelingToolkit.ODESystem(eqs, t, vars, pars, name = :foo)

# equations without variables are forbidden
# https://github.com/SciML/ModelingToolkit.jl/issues/2727
@parameters p q
@test_throws ArgumentError ODESystem([p ~ q], t; name = :foo)
@test_throws ArgumentError ODESystem([p ~ 1], t; name = :foo)

@variables x(t)
@parameters M b k
eqs = [D(D(x)) ~ -b / M * D(x) - k / M * x]
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