[godelski]

You do realize that division is the inverse operation of multiplication, right? Like subtraction is the inverse of addition. By defining addition we define subtraction. By defining multiplication we define division. This is where the author fails. Division is multiplication of a fractional value. This is VERY important.

And just because it is mathematically a field does not mean it is particularly the right choice. A field is not strictly definitely by addition and multiplication, it is definitely by two operators where one is an abelian group (addition in our case) and the other forms and abelian group over the non identity term of the first (eg multiplication is an abelian group over non zero terms). The complex numbers create a field, which is really how we do addition and multiplication in 2D space. 3D space you can't form one, so you have a ring. Which is why quaternions are so important, because they form a field.

But the author is wrong because they think division is a different operation than multiplication. It's just a short hand.

[gowld]

In a field, division by zero is not the inverse operation of anything.

[gjulianm]

The usual definition of division is the multiplicative inverse, yes. But that does not mean that, as an intellectual curiosity (which is how I take this post) you can't define "division" as having other value. Sometimes that's useful, sometimes it's not. Most of the time it is fun to see how things break and don't break. For example, the infamous 1+2+3+... = -1/12 sum[1]: for most purposes it's a divergent sum but you can find ways to assign a finite value and make that useful.

1: https://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B...

[godelski]

The OP says

> The field definition does not include division, nor do our definitions of addition or multiplication.

This is clearly a misunderstanding of not realizing that the definition of division is a symbolic shorthand for inverse multiplication.

Sure, you're right that we can define it another way. But I don't know what we would call an object with three operators. (Someone more knowledgeable in field theory please let me know, it's hard to Google) in the normal field we work with (standard addition and multiplication) we only have two unique operators. Everything else is a shorthand. In fact, even multiplication is a shorthand.

>For example, the infamous 1+2+3... = -1/12

Ramanujan Summation isn't really standard addition though. It is a trick. Because if you just did the addition like normal you would never end up at -1/12, you end up at infinite (aleph 0, a countable infinity). But the Ramanujan Summation is still useful. It just isn't "breaking math" in the way I think you think it is.

But I encourage you to try to break math. It's a lot of fun. But there's a lot to learn and unfortunately it's confusing. But that's the challenge :)

[gjulianm]

The fact that it's a shorthand means that it's not in the definition, just a convention. In fact, nowhere in my studies I saw anyone using 'division' when working explicitly with fields in algebra, it's always multiplicative inverse.

By the way, you cannot do the addition like normal on that series, you don't end up at anything. You can say it diverges and its limit is +infinity (not aleph0, aleph0 is used for cardinality of sets so I think no one would use it as the result of a divergent series). When I said it 'broke math' what I meant was that, in the same way that OP did, it is a way to assign values to things that usually don't have one. I know it does not actually break math.

[jle]

That's not necessarily the definition of division, there are many commonly used definitions in different contracts that are different.

[throwawaymath]

Bravo, that's a great explanation. I think you've done a better job here than my comments elsewhere in this thread. Nice tie in to dimensionality, the complexes and quaternions too.

There are legitimate reasons to advocate for defining division by 0 in the context of a programming language. But the attempt at mathematical rigor really distracts from those reasons. It feels like the author made a decision and reached for some odd mathematics that seems to support it but doesn't. Floating numbers don't even form a field. If we define division by 0 in a field it stops being a field and becomes a ring or some sort of weird finite field with a single element...

[rrampage]

> Division is multiplication of a fractional value

Thus, division by 0 is multiplying by (1/0). Does such a fraction exist? It can go along two potentially different paths depending on the limit we take.

Alternatively, there is information lost when you multiply something by 0: a x 0 = 0, b x 0 = 0. When you perform an inverse by dividing, will you get back a or b (or any number)? Thus, it is not invertible at least at 0.

Disclaimer: Not a mathematician

[godelski]

>Alternatively, there is information lost when you multiply something by 0: a x 0 = 0, b x 0 = 0. When you perform an inverse by dividing, will you get back a or b (or any number)? Thus, it is not invertible at least at 0.

>>A field is not strictly definitely by addition and multiplication, it is definitely by two operators where one is an abelian group (addition in our case) and the other forms and abelian group over the non identity term of the first (eg multiplication is an abelian group over non zero terms).