Talk:Graph of a function

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Topics missing[edit]

I was missing these kind of topics. We should also make a list of famous curves if it isn't yet somewhere in Wikipedia. For instance the Watt's curve in spherical polar coordinates: r2 = b2 - (a sin φ ± √(c2 - a cos2 φ))2 and many more ... --XJamRastafire 19:15 Sep 18, 2002 (UTC)

Another Topic Missing: Graphing Functions. Example: How do you graph the function -3 if x≤-4?

—Preceding unsigned comment added by (talk) 22:42, 19 October 2010 (UTC)

Please, I have read "We can approximate a function --by mean of several methods-- given a functional dependence of adequate size". It seems to me that "Graph of a function" and "Functional dependence" are very closed concepts and clearly represented by a two columns table with a picture like the following:

x | y
5 | 11
2 |  5
1 |  3

Please, let me know if you know such synonym and if so, where is (and who wrote) the original definition of such a type of "functional dependence"? For my part, I know that E. F. Codd in 1972 applied the concept and used the term as a mean of database design verification/normalization. Dr. Amstrong axiomatized this kind of dependences in 1974. I try to found the original mathematical concept before its computer application (if really such thing existed before Codd/Amstrong). Thank you. [Enrique Villar;]

Graph of a function equals the function?[edit]

Article says "In mathematics, the graph of a function f is the collection of all ordered pairs (x,f(x))". The definition given is the definition of a function (so it says that the graph of a function is exactly equal to the function (by set equality)). 07:38, 7 May 2007 (UTC)

That's true if you define functions that way. But I don't think that's a good way to define functions - you really need the codomain as part of the definition, otherwise how can you tell whether or not the function is surjective? See also Function (mathematics)#Is a function more than its graph?. --Zundark 08:56, 7 May 2007 (UTC)

Is it typically y vs x or x vs y?[edit]

Is it typically y vs x or x vs y? —Preceding unsigned comment added by (talk) 05:23, 16 January 2009 (UTC)

What is typically used is y vs. x, such that x is horizontal and y is vertical. However, when specifically talking about plotting a function vs. its input, it is more clear and intuitive to plot f(x) vs. x (or f(y) vs. y or whatever), since the variables x and y are just placeholders. EmergencyBackupChicken (talk) 17:00, 7 May 2009 (UTC)

Graph vs. Plot?[edit]

The term `graph' should really be restricted to use when referring to actual graphs: nodes and edges. The `graph' of a function as described here is really its plot. This is a common misconception that leads to much confusion, and it irks me that it shows up a lot, even in academia. What would be a good way to incorporate this information while still allowing people to find what they are looking for after being told the wrong term? EmergencyBackupChicken (talk) 17:00, 7 May 2009 (UTC)

The word graph is used in both senses in mathematics. I don't think I've ever seen plot used to refer to the graph of a function (as opposed to a graphical representation of the graph of a function). --Zundark (talk) 09:13, 8 May 2009 (UTC)

Merge epigraph and hypograph[edit]

Someone else proposed that Hypograph (mathematics) and Epigraph (mathematics) be merged with each other, but I think they should both be merged here. As far as I can tell from a textbook I looked at briefly, not much can be said about these two notions besides their definition. So I propose to merge them here as derived concepts. JMP EAX (talk) 08:27, 1 August 2014 (UTC)

I would prefer to merge them with each other but not here. For one thing they do have some properties that are different from the graph of a function (e.g. the application to the definition of convex functions). For another, the graph of a function is a topic of great importance in elementary and secondary-school mathematics education and I think adding more advanced concepts such as epigraphs to our article will violate WP:TECHNICAL. —David Eppstein (talk) 01:47, 3 December 2014 (UTC)
I agree with Eppstein. The notion of epigraph is quite unrelated with what is discussed in this page. --Txebixev (talk) 22:25, 25 January 2015 (UTC)
"Someone else proposed"? I have not found this someone else in the corresponding talk pages. --Txebixev (talk) 22:27, 25 January 2015 (UTC)