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Re^5: Algorithm for cancelling common factors between two lists of multiplicands

by tmoertel (Chaplain)
on Aug 11, 2005 at 05:04 UTC ( #482850=note: print w/replies, xml ) Need Help??


in reply to Re^4: Algorithm for cancelling common factors between two lists of multiplicands
in thread Algorithm for cancelling common factors between two lists of multiplicands

The last two digits of the Math::Pari implementation's result seem to be off:
+8.070604647867604097576877675243109941729476950993498765160880e-7030 8.070604647867604097576877675243109941729e-7030 8.070604647867604097576877668E-7030 <-- Math::Pari ^^
Can you increase the implementation's precision? Or is that the limit?

Cheers,
Tom

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Re^6: Algorithm for cancelling common factors between two lists of multiplicands
by BrowserUk (Pope) on Aug 11, 2005 at 05:57 UTC

    The precision is setable, but I had left at the default.

    Increasing the precision to the point where it match or suppassed the accuracy of your Haskell code (a setting of 58), doubled the time it took to a gnat's under 50 ms:

    [ 6:46:43.79] P:\test>MP-FET.pl 8.070604647867604097576877675243109941729476950993498765160880911582E- +7030 1 trial of _default ( 49.865ms total), 49.865ms/trial

    BTW: Could you explain something for me? In this:

    cancel (x:xs) (y:ys) | x == y = cancel xs ys | x < y = let (xs', ys') = cancel xs (y:ys) in (x:xs', ys') | otherwise = let (xs', ys') = cancel (x:xs) ys in (xs', y:ys') cancel xs ys = (xs, ys)

    I understand how it cancels between the lists, but I am confused about when it would pattern match against the second definition?


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      The pattern (_:_) will not match an empty list [], so the first definition will match only when both input lists are non-empty. If one or both of the inputs are empty, the second definition will match.

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