Well, there's no need to apply N Y to zero!
So, for example,
N Y"0] 1 1 2 3 5 8
1 1 1 2 5 21
N Y 20
6765
It took me a while to understand N Y , as I was confusing the right
argument,
the index i of an element ai in the sequence, a0 a1 a2 ... ai ..., with
its value.
N Y actually executes the definition of the general term, ie
ai = a(i-2) + a(i-1)
by means of ($:@<:@<:) + ($:@<:) , which recur on intermediate
decreasing "i" .
The ^:(1 < ]) ensures termination for i in 0 1, and so "defines" a0 =
0, a1 = 1.
Brilliant!
This correspondence has been an eye-opener on $:, which I'd never got the
hang of, as well as an introduction to evoke gerund.
Cheers,
Mike
On 30/11/2018 06:18, Linda Alvord wrote:
Y=: ($:`)(`:6)
N=: 1 :'(u@:<:@:<: + [:u<:)^:(1 < ])'
N=: (5!:1)<'N'
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