# Talk:Blow your mind

### From HaskellWiki

(→List / String Operations: new section) |
(→Polynomial signum and abs: new section) |
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transpose . unfoldr (\a -> toMaybe (not $ null a) (splitAt 2 a)) | transpose . unfoldr (\a -> toMaybe (not $ null a) (splitAt 2 a)) | ||

+ | |||

+ | == Polynomial signum and abs == | ||

+ | |||

+ | A sensible option for signum and abs for polynomials (with coefficients from a field) would be | ||

+ | |||

+ | signum -> the leading coefficient | ||

+ | abs -> the monic polynomial obtained by dividing by the leading coefficient | ||

+ | |||

+ | As with Integer and Data.Complex's abs and signum, the result of signum is then a unit (ie, a value x for which there exists a y such that xy = 1), and we have | ||

+ | |||

+ | signum a * abs a = a | ||

+ | abs 1 = signum 1 = 1 | ||

+ | abs (any unit) = 1 | ||

+ | abs a * abs b = abs (a * b) |

## Revision as of 21:03, 25 August 2012

## 1 Name?

Is there a better name for this page? —Ashley Y 00:55, 2 March 2006 (UTC)

i completely agree, the name pretty much sucks. but what i really wanted, was to compile a collection of "idioms" that would enlarge the readers perception of what is possible in Haskell and how to go about it. so, i'll have to find a name that reflects this plan. —--J. Ahlmann 14:13, 2 March 2006 (UTC)

## 2 List / String Operations

Should this:

transpose . unfoldr (\a -> toMaybe (null a) (splitAt 2 a))

be this instead:

transpose . unfoldr (\a -> toMaybe (not $ null a) (splitAt 2 a))

## 3 Polynomial signum and abs

A sensible option for signum and abs for polynomials (with coefficients from a field) would be

signum -> the leading coefficient abs -> the monic polynomial obtained by dividing by the leading coefficient

As with Integer and Data.Complex's abs and signum, the result of signum is then a unit (ie, a value x for which there exists a y such that xy = 1), and we have

signum a * abs a = a abs 1 = signum 1 = 1 abs (any unit) = 1 abs a * abs b = abs (a * b)