Talk:Polynomial
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Discussion of Polynomial#Graphs
I like this section. I would characterize it as very good but not excellent. It has one shortcoming that I think is easily resolved.
I like the progression of the left side of the page starting with the simplest polynomial (degree zero), including the special case of the x-axis and the more general case, followed by degree 1, 2 etc. Then showing the general case of degree n. I like the parallelism of having formulaic expressions on the left side, and nice looking graphs on the right side.
I have two concerns, one of which is almost trivial:
- why do we have the phrasing "zero polynomial" and "degrees 0 polynomial". not a big deal but slightly confusing. Should degrees be expressed as words or numbers? If both are acceptable maybe we should say so, but mixing numbers and words without explanation is suboptimal
- there's a nice graph for polynomials of degrees 2 through 7, but none for degrees 0 or 1.
I'm trying to decide whether I should be troubled by having formulas on the left for degrees 0,1,2,3,n, while graphs for degrees 2,3,4,5,6,7. I've expressed the desire to add graphs for degrees 0 and 1, should I be troubled that we have a graph for degree for 4,5,6 and 7 but no formula? I'm not troubled but it may be worth discussing.
If others concur, I'll try reaching out to the editor who created the graphics. I think it would be easy to create similar graphics for degrees 0 and 1. if those editors aren't responsive I'll try the graphics lab.--S Philbrick(Talk) 14:36, 18 July 2020 (UTC)
- About '"zero polynomial" and "degrees 0 polynomial"': Earlier in the article we have "The polynomial 0, which may be considered to have no terms at all, is called the zero polynomial". One cannot write "0 polynomial" as this is nowere defined. We could write the "the polynomial 0" instead of "the zero polynomial". But this could introduce a confusion with the degree, which is not zero in this case, but is indefinite. As all degrees that occur here are less than ten, we could use words instead of digit for degrees. This is recommended somewhere by the manual of style. In my opinion, keeping digits makes the classification more visible, and makes clearer the fact zero plays a different role in the two first items. So, my preference is the present version, but my preference is not a rule. D.Lazard (talk) 16:18, 18 July 2020 (UTC)
- I have added graphs of degrees zero and one (those with the closest style that I have found in Commons). IMO, graphs of degrees 6 and 7 should be removed. 16:48, 18 July 2020 (UTC)
- (EC) The difference in names might reflect that the zero polynomial is a proper noun, referring to the unique polynomial with that name. "degree 0 polynomial" is a noun phrase, with "degree 0" being an adjective modifying the noun "polynomial". It would certainly be odd to talk of the "0 polynomial". Using "degree zero polynomial" is less problematic but goes against convention for terse mathematical notation. --Salix alba (talk): 17:06, 18 July 2020 (UTC)
- I agree with D.Lazard and Salix alba. To restate my previous comment, your effort would me more useful if you focused on the real issues instead of bike-shed discussions. --147.229.196.135 (talk)
- Salix alba, Thanks to D.Lazard for adding the graphs for degree zero and degree one. It didn't even occur to me to go check to see if there were suitable examples already. I concur that degree six and degree seven is overkill, not strongly enough to take them out myself but I wouldn't object if they were removed. Excellent point about the fact that the zero polynomial is not a polynomial of degree zero. I was so focused on the lack of parallelism I missed that point. I am aware of the general guidance that digits less than 10 should be spelled out, but I think that applies mostly to articles where the focus is on an issue other than math. I think there is value in using the numerals in this article. S Philbrick(Talk) 14:37, 19 July 2020 (UTC)
- (EC) The difference in names might reflect that the zero polynomial is a proper noun, referring to the unique polynomial with that name. "degree 0 polynomial" is a noun phrase, with "degree 0" being an adjective modifying the noun "polynomial". It would certainly be odd to talk of the "0 polynomial". Using "degree zero polynomial" is less problematic but goes against convention for terse mathematical notation. --Salix alba (talk): 17:06, 18 July 2020 (UTC)
I'm happy to see the addition of graphs for the degree 0 and degree 1 polynomials. At the risk of being anal, we now have four different styles of graphs, obviously because the graphs were created by different people with somewhat different styles.
As a separate issue, the formulas chosen are obviously different from one another, but more so than necessary (unless this is deliberate and I'm missing the reason why). I think that it would be good practice to start with something basic:
f(x)=2
Then keep adding terms:
f(x)=3x+2
Then multiply by, say x-2:
f(x)= 3x^2 -4x -4
- = (3x+2)(x-2)
Possibly adding a scaling value if we want to keep the values within a containment region. Continue mutatis mutandes.
If this makes sense, looking to someone who can help us create the graphs.
Arithmetic – polynomial multiplication
I added two steps to the polynomial multiplication to show the intermediate steps.
I fully understand that people conversant with the subject will find the intermediate steps unnecessary, but many in our audience will find it helpful, and the more advanced we do can skip to the last step easily.
The rest of the section has some issues. It isn't that anything seems wrong, so it's hard to put my finger on it but it doesn't feel very organized. I'm in discussion with another editor about how it can be improved.--S Philbrick(Talk) 14:27, 19 July 2020 (UTC)
Thus a sum of polynomials is always another polynomial
The arithmetic section contains a statement:
Thus a sum of polynomials is always another polynomial.
That statement immediately follows an example. The word "thus" in mathematics is typically a synonym for "therefore" and typically means that the result follows from the immediately preceding statements. I trusted it is obvious that a single example cannot provide proof of a universal claim (obviously, a single example can prove the falsity of a claim but that's not what is at issue here.) Arguably, the word "thus" doesn't simply refer back to the immediately preceding example, but refers to the opening statement of the section:
Polynomials can be added using the associative law of addition (grouping all their terms together into a single sum), possibly followed by reordering (using the commutative law) and combining of like terms
If that's the intention, then it should be moved up but we have other things to discuss.
Arguably, we can claim that while the wording is a little sloppy, the polynomials constitute a set, and it happens to be true that the set is closed with respect to the operations of " addition, subtraction, multiplication, and non-negative integer exponents of variables." I think that's true (I confess I'm rusty), but such a statement requires a reference. There is a reference at the end of the sentence: Polynomials The reference suggests that pages one and two are relevant, which they are, but I reread them twice and don't see anything that makes the claim about the set being closed to those operations.
Additionally, if the set of polynomials is closed to the operations of " addition, subtraction, multiplication, and non-negative integer exponents of variables." we ought to make that statement, with a reference, not simply the statement that (closure exists) with respect to addition.
At a minimum, we need a reference supporting a claim, and separately we need to decide whether to make the claim narrowly about addition or more broadly. Plus, as noted we either need to remove the word "thus" if we want the statement to immediately follow an example, or we need to place it properly in the section.--S Philbrick(Talk) 18:58, 20 July 2020 (UTC)
- You're right about "thus" (which was my addition while un-bulleting). Options are moving it up (but then the example is delayed, which I think is unhelpful), leaving it be (and hoping readers understand that it was supposed to refer back to before the example), or replacing the word "thus" with something else, like "In general" or "As in the example" or simply striking it (although I think that's awkward). --JBL (talk) 21:32, 20 July 2020 (UTC)
I'm trying to keep the terminology as simple as possible. It is understandable that some will feel that saying:
"a sum of polynomials is always another polynomial "
is simpler than saying:
"the set of polynomials is closed with respect to the operation addition"
However, the term " closed" is the mathematical way of making the statement, and there are many many references supporting the claim that polynomials are close with respect to addition (because that's the way it is said) but it's harder to find references to make the arguably simpler statement . For that reason, I introduce the notion of closure, which permitted the addition of a recent reference. — Preceding unsigned comment added by Sphilbrick (talk • contribs) 18:06, 26 July 2020 (UTC)
- It is wrong to use "closed" here, as "closed" is meaningful only for the restriction of an operation to a subset, and, here, the addition in not the restriction of an operation defined on a larger set. You can verify that the word "closed" does not appear in Operation (mathematics). Moreover, your edit does not follow the manual of style. So, I'll revert your edit. D.Lazard (talk) 19:55, 26 July 2020 (UTC)
- D.Lazard, I'm interested in trying to improve mathematics articles. One common complaint is that they are not easily accessible to laypeople, and I hope to work on that but that issue is tangential to this specific issue. I've also noticed that a number of mathematical articles are under-referenced (obviously a more general problem across all our articles). I spend a lot of time at OTRS, where I field inquiries from the general public. (That's one source of the complaints about the relative level of the mathematical articles.) Another issue commonly raised there relates to whether an encyclopedia which can be edited by anyone can be relied upon. My stock answer is a variation of "it cannot. But if you see a statement that's of interest to you, go to the end of the sentence or the paragraph and you will probably find a link to a published reliable source which you may be able to rely upon". Given my stock answer, I thought I'd try to contribute to the solution by digging up references to some of the claims in mathematical articles.
- The sentence in question:
In general, a sum of polynomials is always another polynomial
- Does have a reference after it. However, there is also a hidden comment which I will display here:
- I think that comment is spot on. A reference doesn't have to have the exact wording of the Wikipedia article, but a layperson ought to be able to read the reference and conclude that the sentence in Wikipedia is correct. I read it twice and don't think it's all that obvious.
- For that reason, my initial goal was to find a better reference to support the claim. When I searched, I could find plenty of textbooks asserting that the set of polynomials is closed under addition, but I was struggling to find one that would say that a sum of polynomials is always another polynomial or something very close to that. After thinking about it, I felt I knew why. Mathematicians typically don't say things like a sum of X is another X, they are more apt to say that a set is closed with respect to a particular operation. I decided to take the mountain to Mohammed. If I couldn't find a good source supporting this exact statement, I thought it would be appropriate to introduce the notion of closure, identify that formal mathematical concept is being the same as the more casual "sum of X is another X" and then include a reference that specifically speaks to closure.
- You've objected to that construction. I frankly do not follow:
the addition in not the restriction of an operation defined on a larger set.
- My guess is "in" should be "is" but even if that changes made, I'm not quite following. You also said:
You can verify that the word "closed" does not appear in Operation (mathematics).
- I don't see why that's relevant. That article does talk about the domain of an operation and the range of an operation. That article doesn't go on to talk about situations where the range and domain match, but that's simply because it's beyond the scope of that article. Just off the top my head, that's roughly what we mean by closed — that the range and domain match. However, my point is that when we say that the sum of polynomials is another polynomial, we are saying that the set is closed with respect to the operations of addition. It seems like you dispute that (or something) so can we discuss where we disagree?
- I see you also have concerns about the manual of style but let's resolve the underlying facts and then we can separately decide how best to present them.
- As an important aside, my narrow concern is making sure the claim is properly referenced. If you can track down a reference that suppots the cirrent wording, then I'm not wedded to bringing in the concept of closure into this basic article. If you can't find a reference, I hope you will work with me so that we can rewrite this in a way that it can be properly referenced. S Philbrick(Talk) 21:32, 26 July 2020 (UTC)
- D.Lazard, Just repinging, on the chance you missed this. S Philbrick(Talk) 12:56, 29 July 2020 (UTC)
- The correct use of "closed" can be discussed, but it is not important here, as it is a technical term that is too technical here. If someone is not able to understand "the addition of two polynomials results in another polynomial", it will definively not understand the sentence "the set of polynomials is closed under addition", which involves two technical words ("set" and "closed") that are not useful here. IMO the use of the this phrase in this article is pure pedantry. I always wonder that many people think that using pedantic formulations helps the layman to understand mathematics.
- About referencing. The whole content of section "Arithmetic" appears in hundreds of textbooks. So, I cannot understand why you have difficulties for sourcing that the sum of two polynomials is a polynomial. IMO, it would be worth to add, at the beginning of the section "Arithmetic" a sentence such that "Several operations are defined on polynomial, which are described in the following subsections", followed by a citation of a textbook that define polynomials similarly as here. This would make unnecessary all inline citations in subsections. D.Lazard (talk) 14:27, 29 July 2020 (UTC)
- D.Lazard, I sincerely invite you to find a source that explicitly says that the sum of two polynomials is another polynomial, because all the texts I have consulted make this point implicitly, either via notation or via reference to an algebraic object (a vector space or a ring). --JBL (talk) 15:01, 29 July 2020 (UTC)
- This is not a problem of sourcing, but a problem of wrtiting and logical coherency of the article. Presently, the section begins with "Polynomials can be added ...", which is a very poor definition, as the sentence suggests rather a property. A proper beginning would be: "the addition of polynomials is an operation that takes any two polynomials and produce always another polynomial, and is defined as follows." So, this is not the fact "the sum of two polynomials is a polynomial" that must be sourced, but the definition of the addition of polynomials.
- By the way, it is also interesting to discuss what should be written after "at follows", as this strongly depend on the chosen definition of polynomials. With that of the article, the sum of the polynomials P and Q is simply the expression P + Q. In this case, the example shows that, if the input polynomials are in the normal form of linear combinations of monomials, then the result can be put in a similar normal form by using the method sketched on the example. If one defines a polynomial as a linear combination of monomials, the sketched method describes an algorithm for computing the sum. With other definitions of polynomials, other formulations must be used, but, formally, addition and multiplication should be defined by algorithms.
- For a clear discussion of these questions, I would recommend the book Computer algebra by Davenport, Siret and Tournier. For better sourcing this article, I would suggest to choose one or two textbooks, to write the article in a way that most sentences are compatible with them, and search for sources only for sentences about facts that are not descibed in these books. D.Lazard (talk) 17:18, 29 July 2020 (UTC)
- The section on addition of polynomials should be in principle understandable by a typical 12- or 13-year old. Layering the unnecessary logical structure of a definition including the technical term "operation" is not better in this regard than using vocabulary like "closed" (which I also am trying to avoid).
Here is my view: one should ask "what should a person at level X get out of this section?" If X is "someone who knows what is a vector space, or a ring, or ..." then the answer is "nothing, because they already know what polynomial addition is." So that leaves the possible audience of X as, roughly, people whose knowledge of mathematics ends in secondary school. In my opinion, what they should get out of this section is (1) polynomials can be added, (2) some amount of information about how polynomials actually are added, (3) the observation that the sum of two polynomials is another polynomial, and maybe also (4) an understanding of subtraction of polynomials. Questions about sourcing etc. should be built around meeting those goals, not vice-versa. --JBL (talk) 16:53, 30 July 2020 (UTC)- D.Lazard, Both of you would like to avoid the term "closed". I'm with you, if we can find a solution. It might well be that your proposed formulation:
although it needs some word-smithing, and referencing. Making the assertion that the result of the operation produces another polynomial is a statement requiring a reference. It may seem obvious to the mathematically trained, but not to those who are not (our main audience) and it isn't trivially true; for example, the comparable statement about division is not true.the addition of polynomials is an operation that takes any two polynomials and produce always another polynomial, and is defined as follows.
- I left a request here, although I notice that few recent requests have not been fulfilled. (After rewording and finding a source, I'll cancel the request)S Philbrick(Talk) 13:25, 4 August 2020 (UTC)
- Thanks to both of you.
- I started with D. Lazard's wording, and decided to try:
When polynomials are added together, the result is another polynomial.
- To fit with the tone of the section. As a bonus, that phrasing resulted in a decent source covering more than addition but supporting the claim without the introduction of the word "closed". S Philbrick(Talk) 13:52, 4 August 2020 (UTC)
- The section on addition of polynomials should be in principle understandable by a typical 12- or 13-year old. Layering the unnecessary logical structure of a definition including the technical term "operation" is not better in this regard than using vocabulary like "closed" (which I also am trying to avoid).
- D.Lazard, I sincerely invite you to find a source that explicitly says that the sum of two polynomials is another polynomial, because all the texts I have consulted make this point implicitly, either via notation or via reference to an algebraic object (a vector space or a ring). --JBL (talk) 15:01, 29 July 2020 (UTC)
Summation Notation in Definition Section
I had made some edits which were reverted twice. It was about changing the Summation Notation in Definition Section from:
to
The first one has a domain of all real numbers but 0 (with an indeterminate form 0^0 when x = 0), the second one has domain of all real numbers as is the case with polynomials. I understand that the former is simpler notation but since this is an important fundamental mathematical topic, I would argue that precision should be favoured over simplistic approach. --Niteshb in (talk) 01:17, 18 March 2021 (UTC)