I find it interesting that N-R works for vectors and complex functions (and
mixes of both). Just replace all those scalar functions by their vector
equivalents:

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vn=: 1 : '- n * u %. u D.1'
I added a scaling factor; it makes the convergence slower, but it fixes
problems due to precision-loss.
It works reasonably well:
f=: ^&0 1 - 1 2 ^~ {.
f vn 0.1^:1e3 ] 0 0
1 1
Louis
> On 10 Aug 2017, at 13:07, Martin <d...@famic.de> wrote:
>
> Hi there,
>
> J looks very interesting. I have no previous experience with array
> languages and, being curious, started to experiment. Now, I would
> like to solve a system of non-linear equations. I could only examples
> solving single equations like this one:
>
> N=: 1 : '- u % u d. 1' NB. Adverb implementing Newton-Raphson iteration.
> (_2 + *:) N^:_ ]1 NB. Find root of “0 = _2+x^2”, starting guess of
> “1”.
>
> Is it also possible to solve a system of equation like the following
> one in a similar elegant manner?
>
> f1(x) = a*(1-x1)
> f2(x) = b*(x2-x1^2)
>
> Example from
> https://www.gnu.org/software/gsl/doc/html/multiroots.html#examples
>
> Thanks for any ideas!
> -Martin
>
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