pub unsafe extern "C" fn fdhess(
n: c_int,
x: *mut c_double,
fval: c_double,
fun: fcn_p,
state: *mut c_void,
h: *mut c_double,
nfd: c_int,
step: *mut c_double,
f: *mut c_double,
ndigit: c_int,
typx: *mut c_double,
)