[Haskell-cafe] Re: Unifcation and matching in Abelian groups

[John D. Ramsdell]

The patch avoids a redundant zeroing of c[i].

$ diff -u {a,b}/Main.lhs
--- a/Main.lhs	2009-08-23 21:07:08.000000000 -0400
+++ b/Main.lhs	2009-08-23 21:09:54.000000000 -0400
@@ -255,12 +255,11 @@
 >       --  where n is the length of c.
 >       --    x[n] = sum[j] (c[j] div c[i] * x[j])
 >       --  The new equation to be solved is:
->       --    c[i]*x[n] + sum[j] c'[j]*x[j] = d[k] for all k
->       --  where c'[j] = c[j] mod c[i] for j /= i and c'[i] = 0.
->             let c' = map (\x -> mod x ci) (zero i c)
->                 c'' = divide ci (zero i c)
->                 subst' = eliminate n (i, (invert c'' ++ [1], [])) subst in
->             intLinEqLoop n (c' ++ [ci], d) subst'
+>       --    c[i]*x[n] + sum[j] (c[j] mod c[i])*x[j] = d[k] for all k
+>             intLinEqLoop n (map (\x -> mod x ci) c ++ [ci], d) subst'
+>             where
+>               subst' = eliminate n (i, (invert c' ++ [1], [])) subst
+>               c' = divide ci (zero i c)
 >
 > -- Find the smallest coefficient in absolute value
 > smallest :: [Int] -> (Int, Int)
$