sig
external central : Gsl_fun.gsl_fun -> float -> Gsl_fun.result
= "ml_gsl_diff_central"
external forward : Gsl_fun.gsl_fun -> float -> Gsl_fun.result
= "ml_gsl_diff_forward"
external backward : Gsl_fun.gsl_fun -> float -> Gsl_fun.result
= "ml_gsl_diff_backward"
end