I've written a simple program to calculate determinants of matrices, and while it executes to completion it fails to yield a correct answer. (and yes, I know I'm using lists to represent matrices) I would greatly appreciate any assistance in correcting this algorithm --Carter Schonwald import Prelude first [] = [] first (a:b) = a nth::Int->[a]->a nth _ [] = error "list is too small" nth 1 (a:b) = a nth n (a:b) = nth (n-1) b takeAfter::Int->[a]->[a] takeAfter _ [] = error "list too small" takeAfter 0 a= a takeAfter 1 (a:b) = b takeAfter n (a:b) = takeAfter ( n-1) b type Matrix = [[Rational]] pad a = [x++x| x<- a] time2 [] _ = [] time2 _ [] = [] time2 (a:b) (c:d) = (a * c):(time2 b d) tupleProd (a,b) = a * b altSign a = [b* (-1^num) | b<-a, num <- [2..]] index::Int->Int->Matrix->Rational index a b c = nth b (nth a c) --- ath row, bth column slice::(Int,Int)->(Int,Int)->Matrix->Matrix slice (a,b) (c,d) list = let rowSliceFront = takeAfter (a-1) list --- a and c are rows, b and c are columns in let rowSlice = take (c-a+1) list in let columnSliceFront = map (takeAfter (b-1)) rowSlice in map (take (d-b+1)) columnSliceFront determinant::Matrix->Rational determinant a = det (pad a) (length a) -- only called from determinant det::Matrix->Int->Rational det a 1 = index 1 1 a det a size =let coeffs = altSign (first (take 1 a)) newsize = size - 1 leastToMax = newsize - 1 slices = [ slice (2, i) (size, i + leastToMax) a | i <- [2..(size+1)] ] in sum (time2 coeffs (map (\l-> det l newsize) (map (pad) slices)) )