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How to Read Mathematics

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Re: How to Read Mathematics

#61
post #32
post #2

One thing that I really would like to impress upon computer people is that mathematics is not (usually) a formal computer language. Symbols and technical terms change meaning depending on the author, people write with different "accents". There's a little ambiguity and informality at times, but a whole lot less than other kinds of writing. Mathematics is (usually) written for humans, not computers. Don't attempt to r…

Why is that? Why is there not a universal way of writing mathematics that is not ambiguous and can be read by anyone that understands the 'language'? I have a deep dread and fear of numbers and mathematics in general because I don't understand them and I have never learned. Now I learn that there isn't one thing to learn but a vast array? No thanks. I had this apparently romantic view that an equation is an equation…

What do you mean by "writing" mathematics? The glib answer is that math is a superset of programming and there are non-computable arithmetic functions, so programming is not rich enough to describe what you need to describe when you are talking about math.

I think a more intuitive answer is that in math you are generally talking about relations between infinite sets of objects, whereas in programming you are living in a (in practice) finite space and are evaluating everything into an integer. Programming is about calculating integers, mathematics is about proving theorems. The language has to be very different because what is crucial about evaluating integers unambiguously is peripheral to proving theorems and vice versa.

You can ask, why is it so painful to give a formal proof of correctness of your program? It's impossible to do for all but the most trivial programs. You know that a brilliant person, given years of work, might be able to come up with a proof of correctness, but you also know that the language they would use to do that would be very different from the language that you as programmer would use to write your program. So it goes in both directions. Programs evaluate numbers, they are essentially adding machines, and central to that is the erasure of state via addition.

Math is about symbolic relations and erasure of state is via relations on infinite sets. For example, you want to prove that if a group has a prime number of elements, then it must be cyclic. So pick a generator, raise it to powers, and get a subgroup. Then by Cauchy's theorem, the order of the subgroup has to divide the order of the main group, and that order is prime, so therefore the subgroup has to be the whole group.

There are many things to unpack in that statement. For example, Cauchy's theorem, which says that if a A is a subgroup of B, then the order of A divides the order of B. So

Cauchy's theorem + Group is prime order => non-zero subgroups must be the whole group.

And then every non-zero group has a non-trivial cyclic subgroup + non-zero subgroups must be the whole group => the whole group is a cyclic group.

So it's bit like adding numbers, in that you forget state, but the rules are much more complicated involving quantifiers and a huge universe of sets.

To build a computer that could reason that way, you'd need an infinite set of registers, rules for quantifiers, etc. and your unit of memory would be abstract set relations instead of a zero or 1.

You can try to simulate special cases of that in software, say with an SMT solver. If you look at the DSL of writing code for SMT solvers, it looks different from the code that a programmer is used to writing, and the best SMT solver can't really do anything too interesting from a math point of view, with very rare exceptions.

Moreover in math as practiced, no one (except some logicians) writes in formal logic. It would be too cumbersome. Simple statements like "a harmonic function on a disk achieves its maximum and minimum value on the boundary of its domain" would require thousands of pages of formal symbols and quantifiers. No one can think like that, and so we don't write math that way because we also want to forget things and make compact statements, but what we forget in math is relationships among infinite sets, things like, what are the real numbers, what is a function on the real numbers, what is a differential, what is a harmonic function, what is the maximum of a function, what is a disk, all of that is packed into our statement and replaced with a math statement that is much more compact in the same way that 1 && 0 are replaced by 0 in a computer register, but the computer register is not rich enough to model relations on sets.

Re: How to Read Mathematics

#62
post #32
post #2

One thing that I really would like to impress upon computer people is that mathematics is not (usually) a formal computer language. Symbols and technical terms change meaning depending on the author, people write with different "accents". There's a little ambiguity and informality at times, but a whole lot less than other kinds of writing. Mathematics is (usually) written for humans, not computers. Don't attempt to r…

Why is that? Why is there not a universal way of writing mathematics that is not ambiguous and can be read by anyone that understands the 'language'? I have a deep dread and fear of numbers and mathematics in general because I don't understand them and I have never learned. Now I learn that there isn't one thing to learn but a vast array? No thanks. I had this apparently romantic view that an equation is an equation…

I had this reaction to sign language. Seemed like deaf people missed a good opportunity, but then I realized that how we talk and think is shaped very much by our language. Similarly scholars from different backgrounds have different ways of expressing a precise mathematical concept. This one paper I read implicitly treated complex scalars as real vectors, took me some time to clear up the confusion.

Re: How to Read Mathematics

#63
post #52

> The author usually spends months discovering things, and going down blind alleys. At the end, he organizes it all into a story that covers up all the mistakes (and related motivation), and presents the completed idea in clean neat flow. The way to really understand the idea is to re-create what the author left out. Read between the lines. Pity there's little mathematical writing that actually _does_ contain these b…

I was thinking of ideas for a talk recently, and I thought of "Things I tried that didn't work and one that did" or something to that effect. However, when I looked through my old failed approaches, I found the amount of documentation was proportional to the level of success of the approach, making such a talk nearly impossible.

Re: How to Read Mathematics

#64
post #37

Earlier quoted context omitted.

I worry about the fact that you're being downvoted, because what you're saying is utterly crucial and important. I fear those who ignore it will waste a lot of time with really misguided ways of doing mathematics. The analogy approach works for programming, but it's not applicable to seriously studying mathematics.

> The analogy approach works for programming, but it's not applicable to seriously studying mathematics. Why?

Because in mathematics, unlike programming, you won't get anywhere without actually understanding the topic at hand.

Re: How to Read Mathematics

#65
post #37

Earlier quoted context omitted.

I worry about the fact that you're being downvoted, because what you're saying is utterly crucial and important. I fear those who ignore it will waste a lot of time with really misguided ways of doing mathematics. The analogy approach works for programming, but it's not applicable to seriously studying mathematics.

> The analogy approach works for programming, but it's not applicable to seriously studying mathematics. Why?

Analogies are always leaky abstractions and it's easy to cement an incorrect notion of the subject matter that doesn't account for subtle behavior and edge cases. I do think explaining by analogy is useful as long as it comes with clear caveats, but as an example, if there were good analogies for quantum uncertainty and wave particle duality, or general relativity, people wouldn't find those things eternally perplexing. YouTube has thousands of hours of videos trying to explain GR with elevators in space and trains moving at the speed of light, but if you can't do the math you'll never really understand it. Some things just can't be broken down into concepts that a three dimensional monkey brain can easily understand.

Re: How to Read Mathematics

#66

Earlier quoted context omitted.

Nobody is born knowing how to read effectively. It is a matter of practice and discipline.

Have you actually read any of the papers? While I tend to agree with you in an ideal situation where you may assume the writer is good - that is usually not the case with real-life papers. It's not even the writing per se - it's the structure, or omissions instead. I would rather skim first to find which parts I may not be able to grasp right away and to find out if there's any point spending time on this, rather tha…

> Have you actually read any of the [emphasis mine] papers?

What specific papers are you talking about? TFA doesn't contain a single occurrence of the word “paper”. On the other hand, it contains several occurrences of the word “book”. And, most importantly, it is obviously written for newcomers to mathematics, who for obvious reasons will spend more time reading carefully written books rather than papers written in a rush.

Re: How to Read Mathematics

#67
post #32
post #2

One thing that I really would like to impress upon computer people is that mathematics is not (usually) a formal computer language. Symbols and technical terms change meaning depending on the author, people write with different "accents". There's a little ambiguity and informality at times, but a whole lot less than other kinds of writing. Mathematics is (usually) written for humans, not computers. Don't attempt to r…

Why is that? Why is there not a universal way of writing mathematics that is not ambiguous and can be read by anyone that understands the 'language'? I have a deep dread and fear of numbers and mathematics in general because I don't understand them and I have never learned. Now I learn that there isn't one thing to learn but a vast array? No thanks. I had this apparently romantic view that an equation is an equation…

An exercise that I made during my degree and phd years in maths was to always take notes in a consistent notation across the various lectures, regardless of the convention used by the teacher. It forced me to pay attention and as a bonus I have a consistent set of notes for most undergraduate mathematics :-)

Re: How to Read Mathematics

#68
post #2

One thing that I really would like to impress upon computer people is that mathematics is not (usually) a formal computer language. Symbols and technical terms change meaning depending on the author, people write with different "accents". There's a little ambiguity and informality at times, but a whole lot less than other kinds of writing. Mathematics is (usually) written for humans, not computers. Don't attempt to r…

This is true. The CS folks are my university tended to be quite strict about writing out quantifiers for everything, while a very accomplished math researcher in our department told our class to "please write in English" instead of using those symbols, because he wouldn't be able to read them.

I asked a friend why he thought this was, and he suspected that the CS department's focus on formal languages and automatic theorem proving is what lead to their use of logical symbols.

Re: How to Read Mathematics

#69
post #37

Earlier quoted context omitted.

When you are a student, rather than a researcher, formal definitions must come first, and intuition can be developed later. Otherwise, you are just allowing yourself to say nonsense.

I worry about the fact that you're being downvoted, because what you're saying is utterly crucial and important. I fear those who ignore it will waste a lot of time with really misguided ways of doing mathematics. The analogy approach works for programming, but it's not applicable to seriously studying mathematics.

I wouldn't worry too much about it. Math students are not the primary target audience of this website. And, if the planets align and someone here actually wants to study math, they will either quickly discover the limitations of an “analogy-first” approach, or quickly fail and give up.
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