\[0.0 \lt c_p \land 0.0 \lt c_n\]
\[\frac{{\left(\frac{1}{1 + e^{-s}}\right)}^{c_p} \cdot {\left(1 - \frac{1}{1 + e^{-s}}\right)}^{c_n}}{{\left(\frac{1}{1 + e^{-t}}\right)}^{c_p} \cdot {\left(1 - \frac{1}{1 + e^{-t}}\right)}^{c_n}}\]
\frac{{\left(\frac{1}{1 + e^{-s}}\right)}^{c_p} \cdot {\left(1 - \frac{1}{1 + e^{-s}}\right)}^{c_n}}{{\left(\frac{1}{1 + e^{-t}}\right)}^{c_p} \cdot {\left(1 - \frac{1}{1 + e^{-t}}\right)}^{c_n}}
double f(double c_p, double c_n, double t, double s) {
        double r131506 = 1.0;
        double r131507 = s;
        double r131508 = -r131507;
        double r131509 = exp(r131508);
        double r131510 = r131506 + r131509;
        double r131511 = r131506 / r131510;
        double r131512 = c_p;
        double r131513 = pow(r131511, r131512);
        double r131514 = r131506 - r131511;
        double r131515 = c_n;
        double r131516 = pow(r131514, r131515);
        double r131517 = r131513 * r131516;
        double r131518 = t;
        double r131519 = -r131518;
        double r131520 = exp(r131519);
        double r131521 = r131506 + r131520;
        double r131522 = r131506 / r131521;
        double r131523 = pow(r131522, r131512);
        double r131524 = r131506 - r131522;
        double r131525 = pow(r131524, r131515);
        double r131526 = r131523 * r131525;
        double r131527 = r131517 / r131526;
        return r131527;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019323 +o rules:numerics
(FPCore (c_p c_n t s)
  :name "Harley's example"
  :precision binary64
  :pre (and (< 0.0 c_p) (< 0.0 c_n))

  :herbie-target
  (* (pow (/ (+ 1 (exp (- t))) (+ 1 (exp (- s)))) c_p) (pow (/ (+ 1 (exp t)) (+ 1 (exp s))) c_n))

  (/ (* (pow (/ 1 (+ 1 (exp (- s)))) c_p) (pow (- 1 (/ 1 (+ 1 (exp (- s))))) c_n)) (* (pow (/ 1 (+ 1 (exp (- t)))) c_p) (pow (- 1 (/ 1 (+ 1 (exp (- t))))) c_n))))

Backtrace

get-representation: Unknown representation realLC
(unnamed)/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt653
filter/opt/racket-7.2/collects/racket/private/list.rkt2562
infer-splitpoints/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt340
get-final-combination/data/pavpan/nightlies/herbie/fix-interface-bugs/src/mainloop.rkt3690
(unnamed)/opt/racket-7.2/collects/racket/private/more-scheme.rkt26128
run/opt/racket-7.2/share/pkgs/profile-lib/main.rkt392
profile-thunk16/opt/racket-7.2/share/pkgs/profile-lib/main.rkt90
(unnamed)/opt/racket-7.2/collects/racket/private/more-scheme.rkt26128