2014-08-14 9:44 GMT+02:00 Jon Purdy <evincarofaut...@gmail.com>:
>> Interesting! But what does the (x.) and (-.) words do?
>
> Multiply and subtract in floating point. Factor obviates such
> distinctions with dynamic typing.
Now I get it. With locals your code translates to this in Factor:
:: mean-std-2 ( sum^2 sum inv-len -- mean std )
sum inv-len * dup [ sum^2 inv-len * ] dip sq - sqrt ;
Or without locals:
: mean-std-8 ( inv-len sum^2 sum -- mean std )
pick * -rot * over sq - sqrt ;
Here I rearranged the parameter order to make the stack shuffling more
convenient. Another variant using the tuck word:
: mean-std-6 ( sum^2 sum inv-len -- mean std )
tuck * -rot * over sq - sqrt ;
I must say that the algorithm makes a compelling argument in favor of
locals! Or perhaps in favor of rearranging the parameters to fit the
problem better:
! Fry and tuck
: mean-std-10 ( sum^2 sum inv-len -- std mean )
'[ _ * ] bi@ tuck sq - sqrt ;
I think the last one is fairly readable.
--
mvh/best regards Björn Lindqvist
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