collatz => gen-sequence + collatz-transition

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```;;experiment with COLLATZ-conjecture
;;https://en.wikipedia.org/wiki/Collatz_conjecture

(defun collatz (start-value number-of-value)
(loop repeat number-of-value
with value = start-value

when (evenp value)
do (setq value (/ value 2))
else do (setq value (+ (* 3 value) 1))

collect value))

(list-plot (collatz 15 20)
:zero-based t
:join-points t)

;;;;;;;;;;;;

;;same function like fibonacci-transition but now with COLLATZ.
;;don't know if that makes sense - just a bit code :-)

(defun transition-with-collatz (number-of-values start-val value-a value-b)
(let ((coll-length) (coll-seq) (all-seq))
(setq coll-length (loop
for cnt = 1 then (incf cnt)
collect (sum (collatz start-val cnt)) into bag
when (> (car (last bag)) number-of-values)
do (return (1- (length bag))))
coll-seq (collatz start-val coll-length)
all-seq (append (reverse coll-seq) (loop repeat (- number-of-values (sum coll-seq))
collect 1)))
(loop for i in all-seq
append (loop repeat i
for cnt = 0 then (incf cnt)
when (= cnt 0)
collect value-b else collect value-a))))

;;example-1 => only the process => makes sense when using a lot of values...
(list-plot
(transition-with-collatz 500 56 1 2)
:zero-based t
:join-points t)```

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• 10 months later...

This function will give you the correct result:

```(defun gen-collatz (n)
(prog (value out)
(setf value n)
(setf out (cons value out))
loop
(cond ((eql value 1) (return (nreverse out))))
(setf value
(if (evenp value) (/ value 2)
(+ (* 3 value) 1)))
(setf out (cons value out))
(go loop)))

(gen-collatz 12)
=> (12 6 3 10 5 16 8 4 2 1)

(gen-collatz 27)
=> (27 82 41 124 62 31 94 47 142 71 214 107 322 161 484 242 121
364 182 91 274 137 412 206 103 310 155 466 233 700 350 175
526 263 790 395 1186 593 1780 890 445 1336 668 334 167 502
251 754 377 1132 566 283 850 425 1276 638 319 958 479 1438
719 2158 1079 3238 1619 4858 2429 7288 3644 1822 911 2734
1367 4102 2051 6154 3077 9232 4616 2308 1154 577 1732 866
433 1300 650 325 976 488 244 122 61 184 92 46 23 70 35
106 53 160 80 40 20 10 5 16 8 4 2 1)```

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hi janusz

was there a bug in my code? of course YOU coded it smarter :-)

greetings

andré

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