Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Confusing Notations

  1. Mar 14, 2005 #1
    Does anyone else have trouble with confusing and inconsistent standards of notation in mathematics?

    I am an economics undergrad, and I can't help but think that math would be 1000 times easier if there was just better notation for it. Does anyone know of any radical attempts to create new standards? Or, does anyone know of any learning materials than can help students such as myself "get over" this kind of problem?

    To illustrate, a fundamental example is functional notation.

    f(x) = 5x
    does not reduce to
    f = 5

    It's a mental obstacle for me to think "oh yeah, that 'f' is not a variable." And I have to continuously think it, because my mind is automatically trying to reduce the equation. It drives me nuts. I hope this rudimentary example doesn't make it seem like I'm whining.

    Anyways, thank you for your help! And I look forward to many stimulating discussions on physics (I'm trying to learn the math from Penrose's Road to Reality)
    Last edited: Mar 14, 2005
  2. jcsd
  3. Mar 14, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Unfortunately, the function notation is so standard, that you'd be hard pressed to find any math student (myself included) who thinks there's anything the matter with it. I was introduced to this notation high school and got used to it pretty fast (after working with it for a few months). Nobody ever thinks "multiplication" when they see f(something), and my teacher took pains to make the distinction when he first introduced it. To help you out...when you multiply two variables in algebra...you just stick them next to each other: e.g. xy

    So why the needless parentheses with f(x)? because f is NOT a variable, and this is not multiplication.

    f(x) (read f of x) is a single entity, as those brackets should hopefully clue you in from now on. I hope this helps in that particular case.
  4. Mar 14, 2005 #3
    Maybe writing functions as Mappings from one set to another would help.
  5. Mar 14, 2005 #4
    Thank you, cepheid. I know, my teacher said the same thing.

    I don't think multiplication on the surface, but it's like there's an animal instinct telling me to. And it's a shame, because that animal instinct helped me immensely while in grade school... I did math problems quickly, easily, and efficiently, without even thinking about it. One math teacher felt compelled to give me extra work because I excelled so quickly. And then came functions.

    Maybe my problem is more aesthetic?

    I find it disconcerting because mathematics is supposed to be this bastion of rigorous tools for certainty and unchallengeable deduction. And beauty. But to me much of math looks ambiguous - like a self-destructive chimaera of pieces that have just been grafted on one by one over the years. I'd rather not just rote myself in overlooking certain inconsistencies.

    In your opinion, do you think notations like these might turn students away from math?

    Can you give me an example?
  6. Mar 14, 2005 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    To be honest, I think your problem is just aesthetic...since you seem to be going with your immediate instincts regarding what a mathematical symbol should mean (based on prior experience with things having a similar appearance), rather than consciously thinking about what it has been defined to mean.

    I admit that math notation can get cumbersome, and some notations are better than others, depending on the situation. But what really matters is that in a given context the notation is consistent, so that everyone reading it can understand what it means. I've noticed math texts often take the pains to define everything from beforehand. You spoke of actual inconsistencies in your post, and I'm a bit dubious. Can you think of anything off hand?
  7. Mar 14, 2005 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Actually, in the expression "f(x)", f is a variable -- it's a variable that denotes, say, a general real valued function, as opposed to x which denotes, say, a general real number.

    Interestingly enough, some experts prefer writing fx instead of f(x). (In various contexts, writing xf or even (x)f sometimes occurs) However, a prerequisite for such comfort is the understanding that the real numbers aren't the only game in town. In particular, variables can denote things other than real numbers, and operations like + and * can denote things other than the arithmetic of real numbers.

    What is standardized is that letters like f, g, and h are usually reserved as variables denoting functions and letters like a, b, c, x, y, and z are usually reserved as variables denoting real numbers. (At least in the context with which your familiar)
  8. Mar 14, 2005 #7
    "Context." That's the magic word. There are no inconsistencies if everything fits in its appropriate context.

    Is it too idealistic to ask for a standard notation in all contexts? For instance, that "f" will always and forever be used to describe a function?

    When I was taught grade school algebra, our teacher said very simplistic things, like "letters are just numbers that we don't know." Well, that's just not true with respect to abstract mathematics, and my brain has solidified into looking at letters as stand-ins for numbers.

    I guess I'm expecting there to be some other kind of symbol (maybe a letter from a different alphabet) to describe functions. A similar problem occurs with complex numbers and "i," although that's no where near as bad since an imaginary number is still technically a number. Yeah, it's definitely aesthetic lol.

    Hurkyl, thank you. You described it very well. I guess I just need to "unlearn" what my teacher told me. :)
    Last edited: Mar 14, 2005
  9. Mar 14, 2005 #8
    Yes, it is too much to ask, because different notations suit themselves to different contexts. If you train yourself to do so, it is not that difficult to switch between different meanings for the same notation without much effort(and it is necessary, if you are dealing with many areas of mathematics or physics at the same time).

    I often catch myself writing [tex] {\cal {L}} \{V, \ V \}[/tex], when I mean [tex] {\cal {L}} (V, \ V)[/tex], though!
    Last edited: Mar 14, 2005
  10. Mar 14, 2005 #9
    Okay. I thought it would be reasonable in the Platonic sense. Since math is supposed to exist timelessly and independently of our thoughts on it, what's wrong with giving its symbols timeless and independent meaning?

    Does the necessary ambiguity of some symbols lead us towards constructivism?

    [Edit: I hope that question isn't too off-topic]
  11. Mar 14, 2005 #10
    Well, nothing would be wrong with it. But it would make a lot of things a lot harder to deal with.

    As you stated earlier, the symbols are only ambiguous when you don't specify their context, since they are all defined for each context in which they are used.
  12. Mar 14, 2005 #11
    Math really is like a language, then. I can't get upset over the multiple meanings of a parenthesis anymore than I can get upset over the multiple meanings of the word "fruit."

    Doesn't do much for the Platonist view, then.

    (sorry for turning this discussion towards philosophy)
  13. Mar 14, 2005 #12


    User Avatar
    Science Advisor
    Homework Helper

    actually he is correct that the notation f(x) is inconsistent, and requires an inner knowledge of the context not to be confused with multiplication.

    Mathematica for example is unable to make this association accurately, hence the rules for communicating with that program require us to use square brackets for functional notation and round ones for multiplication.

    e.g. Sin[x] in stead of Sin(x). This would probably solve the difficulties many students have with this as well, but we are stubborn traditionalists and do not like to admit there is a problem if we have ourselves solved it personally.
  14. Mar 15, 2005 #13
    That's true as long as you allow y(x) to also mean multiplication. Which usually is allowed. There's not really a reason to though.
  15. Mar 15, 2005 #14
    Maple, on the other hand, automatically assumes f(x) refers to a function of x, for example.
  16. Mar 15, 2005 #15

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    Sadly there are too many things in mathematics for each to have a unique (and small) symbol. Plus, we often like to use things that are similar to other things exactly because they *do* remind you of something else. And don't you think that other cultures may have an issue if you were to claim the primacy of western orthography?

    Probably, at the point you're talking about you can safely assume that anything labelled by f,g or h is a function, and the letters x,y,z are (real or complex) numbers. In the mathematical alphabet of course, the letter after z is w.... m,n are usually integers, as are p, and q, though these usually are primes, or powers of primes.

    I listened to a talk last year where the lecturer made a good case as to how the evolution of notation has affects the evolution of mathematics itself. The case in point was the realization that one could write functions as diagrams

    [tex] X \rightarrow^f Y[/tex]

    I doubt that will work, but it's supposed to be an arrow from X to Y with the f written above it.
    Last edited: Mar 15, 2005
  17. Mar 15, 2005 #16


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Unfortunately, no. For example, I often see the letters around "f" used to denote elements of groups, or fields, and greek letters are used for functions. (Though, the elements of groups are often functions...)

    However, one usually sees a letter "defined" before it's used, or otherwise made patently obvious from how it's used. For example, a proof might start:

    Let "F" be a field, and let [itex]f \in F[/itex]...

    So, we know that the letter "f" is denoting a general element of "F", and "F" denotes a general field.

    Or, one might have defined the letter "T" to be a linear operator on Rn, in which case once we see T(v) we can infer that v was meant to represent a general element of Rn.
  18. Mar 15, 2005 #17


    User Avatar
    Science Advisor
    Homework Helper

    actually it is impossible to always try to assume that f is a function and x is a variable or input value. i.e. in the expression f(x), either f or x can be the function.

    I.e. a number x, yields a function called "evaluation" on the space of all real valued functions defined on R. thus from this point of view, f is the input, x is the function, and x(f) = f(x) is the output.

    this comes up as soon as one starts to study functional analysis, and dual spaces, and is inescapable. It also raises the issue of "variance", both co and contra.

    In Hurkyl's example above for instance, if T is a linear operator on R^n, and v is a vector in R^n, the expression T(v) still does not reveal which is the function.

    I.e. sending v to T(v) gives a function from R^n to R^n, while sending T to T(v) gives a function from Hom(R^n,R^n) to R^n.

    Thus as Hurkyl says, from knowing the nature of T, one can infer from the expression T(v) that v belongs to R^n, but one can still not always know which function is meant, whether T-->T(v), or v-->T(v).

    Both are important, and which is meant must be specified. (Of course he was assuming there that T had been so specified.)

    This situation arises in the simple concept of a dot product <x,y> where x is a function on y, namely <x,.>, and y is a function on x namely <.,y>.

    Similarly the only thing absolute that can be said above, is there is a natural pairing

    Hom(R^n,R^n) x R^n -->R^n.

    Either factor in the pairing consist of functions on the other factor.

    This is the difference between the two views of tensors that continually compete on these pages. The traditionalists cling to a view of tensors as some kind of huge dot product, and spend time contracting, or evaluating the expressions.

    The modernist thinks in terms of functions on mutually dual spaces.

    I.e. if T is a tangent space, and T* its dual, there is a natural pairing of TxT*-->R. If one artificially defines a dot product, called a riemannian metric, on T, then one also has a (non natural) pairing TxT-->R, by which one can identify T with T* (non naturally).

    Some people fail to observe that this artifice can never serve to alter the nature of elements of T*, i.e. their variance.

    Quite naturally the pairing TxT*-->R yields maps T-->Hom(T*,R), (taking v to evaluation at v)

    or T*-->Hom(T,R), but these maps are essentially the identity.

    Similarly one has natural evaluation plus multiplication pairings TxTxT*xT*-->R, and associated maps T*xT*-->Bil(TxT,R), i.e. one can view elements of T*xT* as a type of tensor. (Some traditionalists argue over whether these tensors are of type (2,0) or type (0,2), whereas to a modernist such notational conventions are of course arbitrary.)

    These relations are all tautological, but become quite complicated when represented by giant arrays of indices.

    In all cases, the intrinsic point of view is merely that T(v) can be viewed either as v-->T(v) or T-->T(v).
    Last edited: Mar 15, 2005
  19. Mar 15, 2005 #18
    mathwonk, that's really interesting about Mathematica. Do you think the evolution of notebook programs like Mathematica will drive the selection process for acceptable standards of notation? And thanks for that second post, even though some of it went over my head. :)

    matt grime,

    Yes! That's exactly what I'm talking about. There are plenty of symbols for us to construct a truly cosmopolitan and "culturally objective" system.

    Are there more concepts in mathematics than there are letters and symbols in all the world's alphabets (excluding the overly complex characters in languages like Chinese)?

    Again, thank you for all your responses. I apologize if my questions seem trivial, but I can't help but feel I'm on to something - that the reason why so many people see math as complicated and confusing is because it isn't written with much of a referable standard. (i.e. it has no dictionary)
    Last edited: Mar 15, 2005
  20. Mar 15, 2005 #19


    User Avatar
    Science Advisor
    Homework Helper

    well my post was too long. As my teacher Lynn Loomis put it:

    when you look at f(p), how do you know f is the function? why couldn't p be the function? I.e. why don't we define p(f) to be f(p)?

    That blew my mind.
  21. Mar 15, 2005 #20
    Math is complicated and confusing. A more consistent notation won't be able to change that significantly.

    Of course, it's still worthwhile to try for a more consistent notation, but you do have to be realistic. Trying to get everyone to use the same notation is like trying to get everyone to use the same language. Even if you could come up with a universal standard that everyone could agree upon, people would still ignore it when obeying the standard got in the way of trying to express something.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook