我需要在F#中用2D实现一个简单的动态编程算法。对于简单的1D案例,Seq.unfold似乎是要走的路,例如, https://stackoverflow.com/a/7986083/5363
是否有一种很好的(有效的)方法可以在2D中实现类似的结果,例如在函数式中重写以下伪代码:
let alpha =
let result = Array2D.zeroCreate N T
for i in 0 .. N-1 do
result.[0, i] <- (initialPi i) * (b i observations.[0])
for t in 1 .. T-1 do
for i in 0 .. N-1 do
let s = row t-1 result |> Seq.mapi (fun j alpha_t_j -> alpha_t_j * initialA.[i, j]) () |> Seq.sum
result.[t, i] <- s * (b i observations.[t])
result
假设所有缺少的函数和数组都在上面定义。
答案 0 :(得分:1)
编辑:实际读取代码,这至少是功能性的,确实有一个稍微不同的返回类型,尽管你可以通过转换避免这种情况
let alpha =
let rec build prev idx max =
match idx with
|0 ->
let r = (Array.init N (fun i -> (initialPi y) * (b i observations.[0]))
r:: (build r 1 max)
|t when t=max -> []
|_ ->
let s = prev |> Seq.mapi (fun j alpha_t_j -> alpha_t_j * initialA.[i, j]) () |> Seq.sum
let r = Array.init N (fun i -> s * (b i observations.[t]))
r:: build r (idx+1 max)
build [] 0 T |> List.toArray