Created
March 17, 2019 22:13
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Deterministic multistage Beverton-Holt model using nested for loops and math/array in Racket
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#lang racket/base | |
(require math/array) | |
;; scalar constants | |
(define years 30) | |
(define prop-female 0.5) | |
(define egg-surv 0.6) | |
;; age-specific fecundity and survival | |
(define fecundity #(0 0 200 400 800)) | |
(define survival #(0.2 0.4 0.6 0.8 0)) | |
(define capacity #(1e6 1e5 1e4 1e3 1e2)) | |
;; multistage Beverton-Holt model | |
(define (beverton-holt N p c) | |
(/ N (+ (/ 1 p) (/ N c)))) | |
;; initialize empty results matrix and make mutable | |
(define results (array->mutable-array (make-array (vector years (vector-length fecundity)) 0))) | |
;; initialize abundances in first year to arbitrary non-zero value | |
(array-slice-set! results (list '(0) (::)) (make-array (vector 1 (vector-length fecundity)) 10)) | |
;; iterate over results to fill matrix | |
(for* ([i (in-range (sub1 years))] | |
[j (in-range (vector-length fecundity))]) | |
;; current abundance vector | |
(define N (array-ref results (vector i j))) | |
;; reproduction | |
(define fecundity-age-j (vector-ref fecundity j)) | |
(when (> fecundity-age-j 0) ;; not all age classes reproduce | |
(define N-female (* N prop-female)) | |
;; next year age-0 | |
(define Nt-age-0 (array-ref results (vector (add1 i) 0))) | |
(define new-age-0 (beverton-holt | |
N-female | |
(* fecundity-age-j egg-surv) | |
(- (vector-ref capacity 0) Nt-age-0))) | |
(array-set! results (vector (add1 i) 0) (+ Nt-age-0 new-age-0)) | |
) | |
;; survival | |
(define survival-age-j (vector-ref survival j)) | |
(when (> survival-age-j 0) | |
(define Nt-age-j (array-ref results (vector (add1 i) (add1 j)))) | |
(define new-age-j (beverton-holt | |
N | |
survival-age-j | |
(- (vector-ref capacity (add1 j)) Nt-age-j))) | |
(array-set! results (vector (add1 i) (add1 j)) (+ Nt-age-j new-age-j)) | |
) | |
) | |
results | |
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