Feature: Implementation of fourier transform

[HanchaiN]

Fix #46

[josdejong]

Nice, this looks good @HanchaiN , thanks a lot!

I made a few inline feedbacks, can you have a look at those?

[josdejong]

Thanks for the updates @HanchaiN , looks good 👍

Two last remarks:

1. Can you remove the usages of math.evaluate from the unit tests? To keep the tests more isolated from the rest of the application (evaluate is pulling in "everything" basically).
2. Can you add type definitions for the two new functions fft and ifft in ./types/index.d.ts, and write tests for it in ./types/index.ts? Then, the functions can be used in TypeScript too.

[josdejong]

Thanks for the updates @HanchaiN. I see the two new TypeScript tests fail because the output is a matrix with a couple of complex values of which the imaginary part is 0 or -0, but the tests fails because the expected outcome are all real numbers. What would be the right outcome?

[HanchaiN]

Apologies for the long break before the update. The test failed when compare {re:1, im:0} and {re:1, im:-0} using assert.deepStrictEqual. However, the function in assert that only approximately compares the value cannot be found. Therefore, the code will be left in this state for a while.

[josdejong]

Ahh, good idea, you could try use approx.deepEqual, I think import * as approx from "../tools/approx.js" should work

[HanchaiN]

It does not work either. But assert.ok(math.deepEqual(...)) might works. Let's try that and see.

[josdejong]

Thanks for the updates @HanchaiN , I see you found a working solution with assert.ok(math.deepEqual(...)) 👍 . Still, it's odd that the outcome is not exactly the same on differing machines (0 or -0), but it's a bit out of scope of this PR I think to figure that out.