Specification

\[\begin{array}{l} \\ \tanh^{-1} x \end{array} \]

(FPCore (x) :precision binary64 (atanh x))

double code(double x) {
	return atanh(x);
}

def code(x):
	return math.atanh(x)

function code(x)
	return atanh(x)
end

function tmp = code(x)
	tmp = atanh(x);
end

code[x_] := N[ArcTanh[x], $MachinePrecision]

\begin{array}{l}

\\
\tanh^{-1} x
\end{array}

Reproduce

herbie shell --seed 2024005 
(FPCore (x)
  :name "Rust f64::atanh"
  :precision binary64
  (* 0.5 (log1p (/ (* 2.0 x) (- 1.0 x)))))

Please file a bug report with this information.

repr->cost: arity mismatch; the expected number of arguments does not match the given number expected: 2 given: 1		L	C
loop	.../private/map.rkt	54	19
f490	.../match/compiler.rkt	548	40
make-alt-table	/home/nightlies/herbie/platforms/src/core/alt-table.rkt	40	0
(unnamed)	/usr/share/racket/collects/racket/contract/private/arrow-val-first.rkt	486	18
initialize-alt-table!	/home/nightlies/herbie/platforms/src/mainloop.rkt	316	0
mutate!	/home/nightlies/herbie/platforms/src/mainloop.rkt	352	0
run-improve!	/home/nightlies/herbie/platforms/src/mainloop.rkt	338	0
get-alternatives/report	/home/nightlies/herbie/platforms/src/sandbox.rkt	169	0
(unnamed)	/home/nightlies/herbie/platforms/src/sandbox.rkt	262	6
(unnamed)	/usr/share/racket/pkgs/profile-lib/main.rkt	40	10
profile-thunk	/usr/share/racket/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/usr/share/racket/collects/racket/engine.rkt	42	24