# Difference between revisions of "Talk:Blow your mind"

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==Name?== |
==Name?== |
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A sensible option for signum and abs for polynomials (with coefficients from a field) would be |
A sensible option for signum and abs for polynomials (with coefficients from a field) would be |
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− | signum -> the leading coefficient |
+ | * signum -> the leading coefficient |

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

+ | |||

+ | As with the abs and signum functions for Integer and for Data.Complex (when restricted to a subring whose intersection with the real numbers is just the integers), the result of this signum is then a unit (ie, a value x for which there exists a y such that xy = 1), and we have |
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+ | |||

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

+ | == Polynomial negate == |
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− | 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 |
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+ | Why not: |
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− | signum a * abs a = a |
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+ | <haskell>negate = map negate</haskell> |
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− | abs 1 = signum 1 = 1 |
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− | abs (any unit) = 1 |
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− | abs a * abs b = abs (a * b) |

## Latest revision as of 12:55, 29 May 2013

## 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)

## 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))

## 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 the abs and signum functions for Integer and for Data.Complex (when restricted to a subring whose intersection with the real numbers is just the integers), the result of this 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)

## Polynomial negate

Why not:

```
negate = map negate
```