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fix bug in partitions function
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86874882e4
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@ -5,8 +5,6 @@
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{-# LANGUAGE TemplateHaskell #-}
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{-# LANGUAGE UndecidableInstances #-}
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{-# OPTIONS_GHC -ddump-splices -ddump-to-file #-}
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module Math.Monomial
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( Mon(..)
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, MonomialBasis(..), Deg, Vars
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@ -188,27 +186,30 @@ partitions :: forall k n
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. Word -- ^ number of parts
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-> Mon k n -- ^ monomial to sum to
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-> [ [ ( Mon k n, Word ) ] ]
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partitions n_parts0 mon0 = go n_parts0 mon0 mon0
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partitions n_parts0 mon0 = go n_parts0 Nothing mon0
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where
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go :: Word -> Mon k n -> Mon k n -> [ [ ( Mon k n , Word ) ] ]
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go :: Word -> Maybe ( Mon k n ) -> Mon k n -> [ [ ( Mon k n , Word ) ] ]
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go 0 _ mon
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| isZeroMonomial mon
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= [ [] ]
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| otherwise
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= []
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go 1 maxSub mon
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go 1 mbMaxMon mon
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| isZeroMonomial mon
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|| mon >= maxSub
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|| case mbMaxMon of { Just maxMon -> mon >= maxMon ; _ -> False }
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= []
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| otherwise
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= [ [ ( mon, 1 ) ] ]
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go n_parts maxSub mon
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go n_parts mbMaxMon mon
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= [ ( part, l ) : parts
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| ( part, l_max ) <- subs mon
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, not ( isZeroMonomial part ) -- parts must be non-empty
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, part < maxSub -- use a total ordering on monomials to ensure uniqueness
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-- use a total ordering on monomials to ensure uniqueness
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, case mbMaxMon of
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Just maxMon -> part < maxMon
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Nothing -> True
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, l <- [ 1 .. min n_parts l_max ]
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, parts <- go ( n_parts - l ) part ( subPart l mon part )
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, parts <- go ( n_parts - l ) ( Just part ) ( subPart l mon part )
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]
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subPart :: Word -> Mon k n -> Mon k n -> Mon k n
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