Implementing Integral

[ericman314]

To go along with the recent additions of simplify and derivative in version 3.9.0, it would be very good to begin implementing integral as well. This issue will discuss ideas on how to do this and how we would like to improve this function over time.

[ericman314]

Here are some ideas to get us started:

1. Use a lookup-table and pattern matching like we do in simplify
2. Implement the insanely complicated Risch Algorithm
3. Quietly forward all calls to integral to Wolfram|Alpha

[josdejong]

I think we should indeed start with your option (1): a relatively simple pattern matching solution.

Option (3) can definitely be interesting! I think this should be a clearly separate set of functions or a separate module which adds the API of wolfram into math.js. Maybe we could integrate the wolfram-alpha library or create an example demonstrating how you can extend math.js with the wolfram api.

[cshaa]

Let's continue the discussion in #1015