In this talk https://www.youtube.com/watch?v=apBWkBDVlow
the presenter attempts to show Haskell hasn't sacrificed speed for
expressiveness by comparing a Java Fibonacci calculator to his Haskell
one.(skip to the 18:00 mark).Essentially, to calculate the 475000th Fibonacci
number, it took his Java program ~8 seconds, while the very terse Haskell
program took ~6 seconds.
So I tried to do the same in J. My first attempt, used a tacit, memoized verb
fib1 =:1:`(($:@:<:) + ($:@:-&2))@.(2&<)M.
However, this gives a stack error for large numbers (~100000). So I decided to
make an imperative verb,
fib2 =: 3 : 0 x1 =. x:1 x2 =. x:1 c =. 0 while. c < y do. tmp =. x1 x1 =. x2
x2 =. tmp + x1 c=.c+1 end. x2
)
This gets there, I can calculate the 475000th Fibonacci number, but
timespacex 'fib2 475000'
36.183 1.31558e6
It takes 36 seconds (of course, my hardware is different to that in the
presentation, but still...).
Is there a speedier way to do this in J? Preferably a tacit one liner would
also be good.
Thanks,
Jon
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