Elliptic integrals in Matlab: symbolic toolbox is slow
My real work in magnetics involves evaluating sometimes complex integrals that often result in solutions that include the elliptic integrals. These are a funny set of functions that I’ve discussed before.
Matlab has historically only included the bare minimum here: in-built function to calculate the first and second complete elliptic integrals. Hence Igor Moiseev’s valuable work in this area (now moved to Github).
Those with a variety of Matlab toolboxes, however, will usually run into the newish functions provided by the symbolic toolbox
ellipticE, and friends. (Quite an impressive collection, actually.) However, if you actually wish to use these functions for something computationally intensive, such as numerical integration, it’s a bad idea to use them. Why?
>> tic; ellipticF(0.5,0.5), toc ans = 0.5105 Elapsed time is 0.020991 seconds.
That’s a small fraction of a second — seems fast! But compare with Igor’s native Matlab function:
>> tic; elliptic12(0.5,0.5), toc ans = 0.5105 Elapsed time is 0.000705 seconds.
So the symbolic toolbox is fine if you just need to evaluate a value or two. But for anything iterative — and this holds for algorithms in general, not just for my own example of numerically integrating elliptic integral functions — you’ll want to avoid the overhead of switching to the symbolic toolbox mid-calculation.
(This is an example of why I find Mathematica a more enjoyable computational environment; no alien toolboxes.)