Exception for Radioactive exchange between two surfaces

Math

\[{x}^{4} - {y}^{4}\]

C

double f(double x, double y) {
        double r7987 = x;
        double r7988 = 4.0;
        double r7989 = pow(r7987, r7988);
        double r7990 = y;
        double r7991 = pow(r7990, r7988);
        double r7992 = r7989 - r7991;
        return r7992;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019191 +o rules:numerics
(FPCore (x y)
  :name "Radioactive exchange between two surfaces"
  (- (pow x 4.0) (pow y 4.0)))

Backtrace

get-representation: Unknown representation #f		L	C
loop	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	122	4
prepare-points	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	146	0
setup-prog!34	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	67	0
run-improve43	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	339	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28