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Added consistency checking for constant-only inequalities and also added a few more useful functions

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Neil Brown 2007-12-14 01:11:29 +00:00
parent 22b09ad95c
commit 57311d8d1e
1 changed files with 20 additions and 1 deletions
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21
transformations/ArrayUsageCheck.hs
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@ -211,9 +211,11 @@ mygcd x y = gcd x y
-- it removes redundant inequalities, fails (evaluates to Nothing) if it finds a contradiction
-- and turns any 2x + y <= 4, 2x + y >= 4 pairs into equalities. The list of such equalities
-- (which may well be an empty list) and the remaining inequalities is returned.
-- As an additional step not specified in the paper, equations with no variables in them are checked
-- for consistency. That is, all equations c >= 0 (where c is constant) are checked to ensure c is indeed >= 0.
pruneAndCheck :: InequalityProblem -> Maybe (EqualityProblem, InequalityProblem)
pruneAndCheck ineq = let (opps,others) = splitEither $ groupOpposites $ map pruneGroup groupedIneq in
mapM checkOpposite opps >>* (\x -> (x,others))
seqPair (mapM checkOpposite opps, mapM checkConstantEq others)
where
groupedIneq = groupBy (\x y -> EQ == coeffSort x y) $ sortBy coeffSort ineq
@ -250,3 +252,20 @@ pruneAndCheck ineq = let (opps,others) = splitEither $ groupOpposites $ map prun
checkOpposite :: (InequalityConstraintEquation,InequalityConstraintEquation) -> Maybe EqualityConstraintEquation
checkOpposite (x,y) | (x ! 0) == negate (y ! 0) = Just x -- doesn't matter which we pick to become the equality
| otherwise = Nothing -- The inequalities can't hold
checkConstantEq :: InequalityConstraintEquation -> Maybe InequalityConstraintEquation
checkConstantEq eq | all (== 0) (tail $ elems eq) = if (eq ! 0) >= 0 then Just eq else Nothing
| otherwise = Just eq
-- | Returns Nothing if there is definitely no solution, or (Just ineq) if
-- further investigation is needed
solveAndPrune :: EqualityProblem -> InequalityProblem -> Maybe InequalityProblem
solveAndPrune [] ineq = return ineq
solveAndPrune eq ineq = solveConstraints eq ineq >>= pruneAndCheck >>= uncurry solveAndPrune
-- | Returns the number of variables (of x_1 .. x_n; x_0 is not counted)
-- that have non-zero coefficients in the given inequality problems.
numVariables :: InequalityProblem -> Int
numVariables ineq = length (nub $ concatMap findVars ineq)
where
findVars = map fst . filter ((/= 0) . snd) . tail . assocs