How to search on this site?

Question

When using this site, it is quite important to be able to find posts on this site which might be related to the question I am interested it - both to avoid duplication (i.e., not asking again questions that have been answered before) and to be able to access useful information already present on the site. However, this task is often quite difficult.

What are good ways to search on this site? Are there some tips and tricks and useful tools which should I know to search efficiently?

^{This post is made with the intention to create a community-maintained FAQ about search. (In particular, a post on meta is easier to edit and update than something in the help center.)}

Answer 1

Approach0

Searching for a specific formula is often rather difficult. A tool which is very suitable for this is the Approach0 search engine.

Some basic information can be found in Guide for New Users (which contains also animations of some examples). If you want to know more about the project, you can look at the documentation.

Approach0 uses mathquill editor and also offers a handy-pad for entering mathematical expressions. But for people familiar with $\rm\LaTeX$/MathJax it might be much easier to enter the expression directly in this form using raw query. (And you can also copy-paste a formula into this field from the source of some post on the site.) You can find some useful information also in the post by the creator of this program: Announcing a third-party search engine for Math StackExchange.

For example, this is what you get if you search for $\sum_{k=1}^n \frac1{k(k+1)}$. You can find many other examples of usage of this search engine if you look at comments and chat messages mentioning Approach0.

Although the "searching" chatroom has a more general purpose, quite a lot of the conversation in that room was devoted to Approach0.

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Some stuff which is useful to keep in mind when using this search engine:

• Recent posts can be missing among the search results - depending on when the index was last updated.
• Approach0 is able - at least to some extent - to find posts where the same expression is written differently. (For example, names of a variables are changed, the sides of an equation are exchanged, etc.) But since this have some limits, you should try to think about various ways of writing the same expression. For example, when looking for posts about limit of Cesàro mean, you could try to search for $\lim_{n\to\infty}\frac{\sum_{k=1}^n a_k}n$, or for $\lim_{n\to\infty} n^{-1}\sum_{k=1}^n a_k$, or for $\lim_{n\to\infty}\frac1n\sum_{k=1}^n a_k)$, or for $\lim_{n\to\infty}\frac{a_1+\dots+a_n}n$ Another example: You get different results if you search for $\lim_{x\to0}\frac{\sin(x)}x$ and if you search for $\lim_{x\to0}\frac{\sin x}x$.
• There is a distinction between \infty and +\infty. For example, you get different results for $\lim_{x\to\infty} (1+\frac1n)^n$ and for $\lim_{x\to+\infty} (1+\frac1n)^n$ then the results are completely different.
• There is also a distinction between |x| and \left|x\right|, Approach0 treats these two differently as a result of some technical considerations. For example, compare the search for $\frac{|x+y|}{1+|x+y|}\le\frac{|x|}{1+|x|}+\frac{|y|}{1+|y|}$ with and without including \left and \right.

Answer 2

Lists of questions

There are also various lists of questions which might help when searching for some topic (some of them generated by the Stack Exchange software, some of them created manually).

• If you click on ask question and fill at least the title (perhaps also tags) the software generates a list of questions that are similar. As pointed out by some users, this can be used basically as a search engine. See also: Trying to ask a question provides better results than normal search.
• If you have already found a question which is close to what you are looking for (although perhaps not the exact fit), it might be useful to check also the linked and related questions which are shown in the sidebar on the right. Typically, they tend to be rather similar to the question you are currently viewing.

The following is useful mainly if you are looking for a problem which is rather common and you suspect that it has very likely been asked before.

• There are some lists of frequently asked questions which were collected by users of this site. Mainly List of Generalizations of Common Questions and Catalog of standard exercises. Some of posts from specific areas can be found here: Would “organizer posts” be useful/welcome here?

Answer 3

Google

You can simply use Google with the restriction to this domain, using (in addition to the search query) site:math.stackexchange.com. (Of course, you can also use any other search engine where this restriction is possible.) For example, you can use the search: triangular numbers site:math.stackexchange.com to get to relevant posts about triangular numbers.

Google indexes the whole page, which means that it searches for the keywords both in posts and in comments. Another possible advantage is that the ranking of results is provided by Google. (You might find the ordering chosen by Google better than the one obtained from built-in-search. It takes into account different things - depending on your preferences you might be more satisfied with this one.)

Sometimes also using Google Images might be useful. (For example, if you have seen the problem on the site before and remember that the question on the answer had picture. Or if you simply know that the solution can be illustrated by a nice picture.) Some examples: harmonic series site:math.stackexchange.com or cobweb plot site:math.stackexchange.com.

A few other examples showing Google being used when searching for a specific problem can be found here: How to search math terms/notations accurately and efficiently? Could some experienced users summarize some tips here? and How to google search mathematical notions and expressions?

Answer 4

Built-in-search

The site has built-in search engine - the search bar is near the top of the site. Notice that after you get to search results a link with "Advanced Search Tips" become available - it contains various search modifiers. (Advanced search options can also be found in the help center.)

Some useful advice:

• Notice that search results can be sorted in various ways (relevance, date of posting, score of the post, date of the most recent activity).
• In this way you search only in posts - not in comments. (If you need to search in comments, you can find some advice in: Searching comments and How to browse or search comments?)
• Tags can be used to restrict your search. For example, instead of searching for all posts containing the name Pascal you can restrict the search to the posts tagged (binomial-coefficients), if this is what you are interested in.
• Notice that if you search only using tags, then also the frequent tab becomes available. It lists the questions that have most links from/to other posts. For example, if you are looking for a question which is about some sum with binomial coefficients, then it is quite likely that it might be tagged both (binomial-coefficients) and (summation). If you suspect that it is a basic question which might have been asked several times in the past, you could try to go to questions having these two tags and then choose the frequent tab.
• Similarly, frequently asked questions tend to have many views, so if you are looking for such questions you can restrict the search to posts with large number of views, for example: Pascal views:1000.

See also:

• If you browse through the posts tagged search here on meta, you can find plenty of useful information about searching. (In particular, some tips and tricks which might by useful in some situations.)

Answer 5

Math search engines

There are various tools online specifically for searching for mathematical content. Approach0 is already mentioned in a separate answer. Some other search engines include:

• SearchOnMath which includes searching on several sites, including Mathematics Stack Exchange, MathOverflow and others. For example, here is search for $\sum_{k=1}^n \frac1{k(k+1)}$. It was mentioned also on meta and on the main site.