Because rk4M started also with an accumulating fold, the next version
will be:
p4=: 1 :(':';'({:y)+6%~+/1 2 2 1*(x*[: u y+(*x&,))/\.1 0.5 0.5,x*u y')
rk4M=: 1 :0
'Y0 a b h'=. 4{. y
(,.[:h&(u p4)@,/\.Y0,~}.)&.|. a+i.@>:&.(%&h) b-a
)
>
> (*x&,@{:)
>
> was used in an earlier attempt with an accumulating fold. It can be
> simplified (because of using the faster scan fold) to
>
> (*x&,)
>
--
Met vriendelijke groet,
@@i = Arie Groeneveld
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