```{index} single: fibonacci; PDL::Primitive function ``` ```{index} single: PDL::Primitive::fibonacci; Perl function ``` # fibonacci `fibonacci($n_or_pdl)` -- Fibonacci sequence constructor. Mirrors upstream `PDL::fibonacci` (`Primitive.pd` `pp_def 'fibonacci'`, `Pars => 'i(n); [o]x(n)'`). The engine op `pdl_run_fibonacci(i, x)` writes `x[k] = x1+x2` with `x1=1, x2=0` initially and the standard carry `{ x2=x1; x1=x[k] }` from `k>0`, producing `1,1,2,3,5,8,13,...`. Two call forms, mirroring upstream's `PDL::fibonacci` wrapper: - `fibonacci(N)` — scalar integer → N-element pdl - `$pdl->fibonacci` — fills `$pdl` in-place (inplace flag) The connector prepares the `i` input pdl (a sequence of counter values, shape-match the desired output) and lets the engine do the actual recurrence.