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Fixed a bug in the solveUnits function where everything was always being negated, when it should be dependent on whether the unit coefficient was 1 or -1

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Neil Brown 2007-12-12 17:24:50 +00:00
parent 76dc1c3b53
commit 94dca6fc10
1 changed files with 20 additions and 8 deletions
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28
transformations/ArrayUsageCheck.hs
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@ -112,14 +112,26 @@ solveConstraints p ineq
scaled_x_k_val = amap (* (eq ! k)) x_k_val
solveUnits :: EqualityProblem -> StateT InequalityProblem Maybe EqualityProblem
solveUnits p = case findFirstUnit p of
(Nothing,p') -> return p' -- p' should equal p anyway
(Just (eq,ind),p') -> modify change >> solveUnits (change p')
where
change = substIn ind (arrayMapWithIndex (curry $ negateOthers ind) eq)
negateOthers :: CoeffIndex -> (CoeffIndex,Integer) -> Integer
negateOthers match (ind,val) = if match == ind then 0 else negate val
solveUnits p
= case findFirstUnit p of
(Nothing,p') -> return p' -- p' should equal p anyway
(Just (eq,ind),p') -> modify change >> solveUnits (change p')
where
change = substIn ind (arrayMapWithIndex (modifyOthersZeroSpecific ind) eq)
origVal = eq ! ind
-- Zeroes a specific coefficient, modifies the others as follows:
-- If the coefficient of x_k is 1, we need to negate the other coefficients
-- to get its definition. However, if the coefficient is -1, we don't need to
-- do this. For example, consider 2 + 3x_1 + x_2 - 4x_3 = 0. In this case
-- x_2 = -2 - 3x_1 + 4x_3; the negation of the original equation (ignoring x_2).
-- If however, it was 2 + 3x_1 - x_2 - 4x_3 = 0 then x_2 = 2 + 3x_1 - 4x_3;
-- that is, identical to the original equation if we ignore x_2.
modifyOthersZeroSpecific :: CoeffIndex -> (CoeffIndex -> Integer -> Integer)
modifyOthersZeroSpecific match ind
| match == ind = const 0 -- The specific value to zero out
| origVal == 1 = negate -- Original coeff was 1; negate
| otherwise = id -- Original coeff was -1; don't do anything
findSmallestAbsCoeff :: EqualityConstraintEquation -> CoeffIndex
findSmallestAbsCoeff = fst. minimumBy (cmpAbsSnd) . filter ((/= 0) . snd) . tail . assocs