racket recursion video 5/6 --- manual memoization
Channel: Danny Heap
Date: 2012-06-03

http://www.cdf.toronto.edu/~heap/racket_lectures.html   Video on Serpinski's triangle, a fractal, most naturally rendered with recursion.  There's an efficiency problem, since recursive calls are computed redundantly.  This is solved by memoization --- recording computations the first time they are encountered.  See also:

www.cdf.toronto.edu/~heap/Racket/recursion.html    You should also look at:
www.cdf.toronto.edu/~heap/racket_lectures.html