Fix and test derivative(x, 2x) #1078
Conversation
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It's a unityper type https://github.com/YingboMa/Unityper.jl So you need to check the EXPR type https://github.com/JuliaSymbolics/SymbolicUtils.jl/blob/d68e092a646ee746becc16fa5ec0e7e066a96f12/src/types.jl#L252 |
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This breaks |
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I am fine with having more errors, more safety. |
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This also breaks differentiating with respect to an array of symbols (which we should presumably fix) and with respect to |
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The crux of this issue is that we assume two expressions are constant with respect to eachother unless proven otherwise. julia> @variables x, y
julia> Symbolics.derivative(x, y)
0This PR does not fix that issue, and does introduce errors which previously worked e.g. all of these results will become errors: |
src/diff.jl
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| @@ -31,8 +31,13 @@ julia> D3 = Differential(x)^3 # 3rd order differential operator | |||
| """ | |||
| struct Differential <: Operator | |||
| """The variable or expression to differentiate with respect to.""" | |||
| x | |||
| Differential(x) = new(value(x)) | |||
| x::BasicSymbolic | |||
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We shouldn't limit it to BasicSymbolic
src/diff.jl
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| x::BasicSymbolic | ||
| function Differential(x) | ||
| vx = value(x) | ||
| vx isa BasicSymbolic && SymbolicUtils.exprtype(vx) == SymbolicUtils.SYM || |
| Differential(x) = new(value(x)) | ||
| function Differential(x) | ||
| vx = value(x) | ||
| istree(vx) && throw(ArgumentError("Cannot differentiate with respect to $vx")) |
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This is also not quite correct. We frequently need to differentiate wrt variables with an independent variable like x(t).
Fixes #1077