Others have already given elegant solutions, but if you'd like a simple
transliteration that does not require a struct, here you go:
#lang racket
(require math)
(define (logmod y r k thetasd)
(define theta (flvector-ref (flnormal-sample 0.0 thetasd 1) 0))
(list (* y
(- r (* r (/ y k)))
(exp theta))
r k thetasd))
(define (project-pop y r k thetasd t [i 1])
(if (= i t)
(list y)
(cons y (apply project-pop (append (logmod y r k thetasd) (list t (+
i 1)))))))
(project-pop 1.0 1.8 20.0 0.1 25)
====================
If you'd like to reduce it to one function, you could do this:
(define (project-pop y r k thetasd t [i 1])
(if (= i t)
(list y)
(cons y (project-pop (let ([theta (flvector-ref (flnormal-sample 0.0
thetasd 1) 0)])
(* y (- r (* r (/ y k))) (exp
theta)))
r k thetasd t
(+ i 1)))))
(project-pop 1.0 1.8 20.0 0.1 25)
On Thu, Apr 11, 2019 at 1:50 AM <travis.hinkel...@gmail.com> wrote:
> Hi All,
>
> I'm trying to better understand recursion. I decided to rewrite the
> logmodr function from this blog post
> <http://www.seascapemodels.org/rstats/2017/02/26/speeding-up-sims.html> as
> a recursive function. I was easily able to write the recursive functions if
> all but one of the arguments were set to default values. But I was
> completely stumped by how to handle the situation without using default
> argument values. After a considerable amount of flailing about, I finally
> realized that I could accomplish this task by passing the arguments as a
> struct (see code below). I find the struct approach relatively intuitive
> but it strikes me as quite verbose. Are there other (better?) ways to
> handle this task?
>
> Thanks,
>
> Travis
>
>
> #lang racket
>
> (require math)
>
> (struct args (y r k thetasd) #:transparent) ; only 'y' changes in
> project-pop function below
>
> (define (logmod args-struct)
> (define theta (flvector-ref (flnormal-sample 0.0 (args-thetasd
> args-struct) 1) 0))
> (args (* (args-y args-struct) (* (- (args-r args-struct) (* (args-r
> args-struct) (/ (args-y args-struct) (args-k args-struct)))) (exp theta)))
> (args-r args-struct)
> (args-k args-struct)
> (args-thetasd args-struct)))
>
> (define (project-pop args-struct t [i 1])
> (define y (args-y args-struct))
> (if (= i t)
> (list y)
> (cons y (project-pop (logmod args-struct) t (+ i 1)))))
>
> (project-pop (args 1.0 1.8 20.0 0.1) 25)
>
>
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