For the benefit of other beginners, I think there was a small typo in
prop-projection.v1 where the intention was to call that function
recursively rather than calling pop-projection in the body of
pop-projection.v1. The typo is corrected below:
(define (pop-projection.v1 A n iter)
(if (zero? iter)
(list n)
(cons n (pop-projection.v1 A (matrix* A n) (- iter 1)))))
Thanks to everyone for the feedback. It has been very illuminating!
On Sunday, February 10, 2019 at 5:49:01 PM UTC-8, Matthias Felleisen wrote:
>
>
>
> On Feb 10, 2019, at 7:26 PM, Alex Harsanyi <alexha...@gmail.com
> <javascript:>> wrote:
>
> One way to do this is for `pop-abundances` to have an extra parameter, the
> list of previous abundances, and whenever the function is called
> recursively, it adds the current abundance to this list and passes it on to
> the next call. The final call will than return this result instead of the
> last abundance. In the example below, "cons" adds to the front of the
> list, so "result" contains the most recent values first and this list is
> reversed before being returned to the user. Also, when `pop-abundances` is
> invoked by the user, there are no "previous abundances" , so it needs to be
> invoked with an empty list -- this is handled by a default parameter for
> 'result':
>
> #lang racket
> (require math/matrix)
>
> (define A (matrix [[0 0 5.905]
> [0.368 0.639 0.025]
> [0.001 0.152 0.051]]))
>
> (define n (col-matrix [5 5 5]))
>
> (define (pop-projection A n iter [result '()])
> (if (zero? iter)
> (reverse (cons n result))
> (pop-projection A (matrix* A n) (- iter 1) (cons n result))))
>
> (pop-projection A n 25)
>
>
>
>
> Don’t use accumulators if the function has all the information:
>
> #lang racket
>
> (require math/matrix)
>
> (define A
> (matrix
> [[0 0 5.905]
> [0.368 0.639 0.025]
> [0.001 0.152 0.051]]))
>
> (define n (col-matrix [5 5 5]))
>
> (define (pop-projection A n iter [result '()])
> (if (zero? iter)
> (reverse (cons n result))
> (pop-projection A (matrix* A n) (- iter 1) (cons n result))))
>
> (define (pop-projection.v1 A n iter)
> (if (zero? iter)
> (list n)
> (cons n (pop-projection A (matrix* A n) (- iter 1)))))
>
> (equal? (pop-projection A n 25) (pop-projection.v1 A n 25))
>
>
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