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Assigning symbolic SparseArrays fails #6
Description
If I want to have a multi-dimensional sparse array. I could define
using Symbolics
using SparseArrayKit
@variables a
A = SparseArray{Num}(undef, (1,2,3)) #3dimesional array with size 1, 2, and 3 each
A[1,1,1] = a
But this gives the well-known error
ERROR: TypeError: non-boolean used in boolean context
This is due to the fact that in line #34 of sparsearray.jl we have the zero-comparison if v != zero(v).
This however fails for symbolic expressions as == or != defines an equation.
In this context, one should use if v !== zero(v) to evaluate the expression. Then everything works and still works for regular numbers.
Activity
maartenvd commentedon Dec 21, 2022
Sorry for the late reply, I totally forgot about this issue!
that line really should've used iszero, can you verify that everything (the minimal example you provide works, but presumably you do other operations as well) works on the latest master?
davidschlegel commentedon Jan 10, 2023
The problem is that for symbolic numbers that are defined through
Symbolics.jlthe functioniszerodoes not have a boolean output but rather defines an equation. Therefore, one should use the double-==to check if symbolic expressions are literally zero.davidschlegel commentedon Jan 10, 2023
#7
Jutho commentedon Jan 10, 2023
I am not familiar with Symbolics.jl, but I have to admit that this seems wrong. The documentation of
Base.iszeroliterally states that "Return true ifx == zero(x)". If Symbolics.jl choses to have different behaviour, then this is not a method extension of Base.iszero, and thus, it should be a different function.davidschlegel commentedon Jan 11, 2023
Sorry, I got confused myself for a second.
From the julia documentation for
===:Indeed, Symbolics.jl has the behavior that for a symbolic variable,
x==0defines an equation, whileisequal(x, 0)gives a boolean.I think, instead of fiddling with
==and===and their negations, one could useisequalto prevent all issues with of non-numeric types.Jutho commentedon Jan 11, 2023
I had anticipated that, but one problem with using
===orisequalis that, with floating point numbers,returns
false.davidschlegel commentedon Jan 11, 2023
Okay, in that case, I would stick to
===and!==instead of==and!=.Jutho commentedon Jan 11, 2023
Well, but these have the same problem. Also
-0. === +0.is false, or thus-0.would not be recognised as a zero entry. I don't know how troublesome that would be in practice.davidschlegel commentedon Jan 11, 2023
I agree, then, it is a matter of non-numerical types to adequately define
iszero. Submitted an issue inSymbolicUtils.jlfor this. This is already working forNumtypes but not forSymtypes.