Segmentation error with sparse arrays

[MarcBerliner]

It was difficult to find an MWE since Julia just kept crashing:

using Symbolics, SparseArrays

@variables x y[1:4]

z = Symbolics.Num[
    0
    -x*((1//3)*y[1] + (1//12)*y[2] + (1//6)*y[3] + (1//9)*y[4])*((y[1] + y[2] + y[3] + y[4])^-1)
]

sparse(z)
zsh: segmentation fault  /Applications/Julia-1.6.app/Contents/Resources/julia/bin/julia

If you use convert

convert(SparseVector{Num, Int64},z)
ERROR: StackOverflowError:
Stacktrace:
      [1] promote_type
        @ ./promotion.jl:233 [inlined]
      [2] promote_result(#unused#::Type, #unused#::Type, #unused#::Type{DynamicPolynomials.Term{true, Any}}, #unused#::Type{Any})
        @ Base ./promotion.jl:247
--- the last 2 lines are repeated 79982 more times ---
 [159967] promote_type
        @ ./promotion.jl:233 [inlined]

Interestingly, if you remove the negative sign on x it works just fine.

I'm using Symbolics v3.2.3.

[MarcBerliner]

Fixed by JuliaAlgebra/MultivariatePolynomials.jl#175

[moble]

A workaround would be to define

y = [Symbolics.variable(:y, i) for i in 1:4]

I don't think this should be necessary, though; see #379.