Re: [Haskell-beginners] List operations

x ** y = 10 ** (y * logBase 10 x) Much easier to do base 10 exponents. *Euler025> 25.0 ** 3.5 78125.0 *Euler025> 10 ** (3.5 * logBase 10 25.0) 78125.00000000009 On Thu, May 19, 2011 at 9:15 AM, Ertugrul Soeylemez wrote:

Daniel Fischer wrote:

...

However, since you're asking about cost, which indicates that you care for performance, the above would be better written as

[x*x*x | x <- list]

unless you depend on the small differences in the outcome [I'm not quite sure how many bits may be affected, not many, typically none or one].  Functions like (**), exp, log, sin, cos, ... are slow, very slow.  If the exponent is a small (positive) integer, specifically giving a sequence of multiplication steps is much faster, also using (^) instead of (**) is faster for small exponents (but slower than an explicit multiplication sequence).

Neither does this really match my intuition, nor can I confirm it with an experiment.  Applying (** 3) a million times to a Double takes a second and gives me the expected Infinity.  Applying (^3) or (\x -> x*x*x) a million times to the same value, well, I didn't want to wait for it to finish.

The experiment was ran with the following codes in GHCi:

   iterate (** 3) 1.000000001 !! 1000000    iterate (^3) 1.000000001 !! 1000000    iterate (\x -> x*x*x) 1.000000001 !! 1000000

Note that exponentiation is a cheap operation on Double.

Greets Ertugrul

-- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

-- -- Regards, KC