Here's a recursive solution.
( Following the solution you'll see that I am still somewhat mystified
about $: and f. . )
Write an implicit recursive verb for this sequence formula:
a1 , (a2=.1-~2*a1) , (a3=.1+~2*a2) , (a4=.1-~2*a3) , (a5=.1+~2*a4) ...
(an=.1(+-)~2*an-1
The result will be a vector n items long. Note the alternating sign in each
term
x is the number of terms
y is the current sequence
Example:
5 f 4
4 7 15 29 59
_____________________
A solution, I still love hooks
_____________________
agenda =: (> * [: >: 2&|) #
assert 2 -: 4 agenda 4 4 43 NB. odd length use 3rd verb
assert 1 -: 4 agenda 4 4 NB. even use 2nd verb
assert 0 -: 4 agenda 4 4 8 8 8 NB. complete use 1st verb
assert 0 -: 4 agenda 4 4 8 8 NB. complete
complete =: ]
f_odd =: $: (, 1 2 p. {:)
f_even =: $: (, _1 2 p. {:)
f =: (complete f.)`(f_odd f.)`(f_even f.)@.agenda
assert 4 7 15 29 59 -: 5 f 4
------------------------
NB. stack error because $: limits scope to the adverb
f =: complete`f_odd`[email protected]
NB. I'm rather clueless about this fixed expansion, which also produces
stack error
complete`f_odd`[email protected] f.
]`(3 : '$: (, (_1 2 p. {:)) y' :(4 : 'x $: (, (_1 2 p. {:)) y'))`(3 : '$:
(, (1 2 p. {:)) y' :(4 : 'x $: (, (1 2 p. {:)) y'))@.((> * [: >: 2&|) #)
> Message: 1
> Date: Tue, 27 Nov 2018 01:09:30 -0600
> From: Skip Cave <[email protected]>
> To: "[email protected]" <[email protected]>
> Subject: [Jprogramming] Recursive verbs
> Message-ID:
> <
> caj8lg_ejjn3lbmvhppawbdox0s65vffvja4shpj_nmv-ehp...@mail.gmail.com>
>
>
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