Add C++ cbrt() function for reals (FreeFem#352)

Author: cmdoug

src/fflib/AFunction.cpp

@@ -1627,6 +1627,7 @@ void Init_map_type()
 
      Global.Add("atan","(",new OneOperator2<double>(atan2));
      Global.Add("sqrt","(",new OneOperator1<double>(sqrt,2));
+     Global.Add("cbrt","(",new OneOperator1<double>(cbrt,2));
      Global.Add("abs","(",new OneOperator1<double>(Abs));
      Global.Add("abs","(",new OneOperator1<long>(Abs));
      Global.Add("cos","(",new OneOperator1_<Complex>(cos));

src/fflib/array_real.cpp

@@ -47,6 +47,7 @@ void initArrayOperatordouble() {
   Add<KN_rmeps<K> >("(","",new OneOperator2<KN_<K>,KN_rmeps<K>,double>(rmeps));
   Global.Add("fabs", "(", new OneOperator1F_KN_<F_KN_<K, K, K, KK>, K, KK, KN_<K> >(fabs));
   Global.Add("abs", "(", new OneOperator1F_KN_<F_KN_<K, K, K, KK>, K, KK, KN_<K> >(fabs));
+  Global.Add("cbrt","(",new OneOperator1F_KN_<F_KN_<K,K,K,KK>,K,KK,KN_<K> >(cbrt));
   Global.Add("acos", "(", new OneOperator1F_KN_<F_KN_<K, K, K, KK>, K, KK, KN_<K> >(acos));
   Global.Add("asin", "(", new OneOperator1F_KN_<F_KN_<K, K, K, KK>, K, KK, KN_<K> >(asin));
   Global.Add("atan", "(", new OneOperator1F_KN_<F_KN_<K, K, K, KK>,K, KK, KN_<K> >(atan));