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 // -*- C++ -*-
 #ifndef RIVET_Utils_HH
 #define RIVET_Utils_HH
 
 #include "Rivet/Tools/RivetSTL.hh"
 #include "Rivet/Tools/TypeTraits.hh"
 #include "Rivet/Tools/PrettyPrint.hh"
 #include "Rivet/Tools/Exceptions.hh"
 #include <ostream>
 #include <cctype>
 #include <cerrno>
 #include <stdexcept>
 #include <numeric>
 #include <limits>
 #include <climits>
 #include <cfloat>
 #include <cmath>
 #include <sstream>
 #include <functional>
 
 /// @defgroup utils Other utilities
 
 
 /// Macro to help mark code as deprecated to produce compiler warnings
 #ifndef DEPRECATED
 #if __GNUC__ && __cplusplus && RIVET_NO_DEPRECATION_WARNINGS == 0
   #define DEPRECATED(x) __attribute__((deprecated(x)))
 #else
   #define DEPRECATED(x)
 #endif
 #endif
 
 
 namespace Rivet {
 
 
   /// Convenient const for getting the double NaN value
   static constexpr double DBL_NAN = std::numeric_limits<double>::quiet_NaN();
 
 
   /// @defgroup strutils String utils
   /// @{
 
   /// @brief Exception class for throwing from lexical_cast when a parse goes wrong
   struct bad_lexical_cast : public std::runtime_error {
     bad_lexical_cast(const std::string& what) : std::runtime_error(what) {}
   };
 
   /// @brief Convert between any types via stringstream
   template<typename T, typename U>
   T lexical_cast(const U& in) {
     try {
       std::stringstream ss;
       ss << in;
       T out;
       ss >> out;
       return out;
     } catch (const std::exception& e) {
       throw bad_lexical_cast(e.what());
     }
   }
 
   /// @brief Convert any object to a string
   ///
   /// Just a convenience wrapper for the more general Boost lexical_cast
   template <typename T>
   inline string to_str(const T& x) {
     return lexical_cast<string>(x);
   }
 
   /// @brief Convert any object to a string
   ///
   /// An alias for to_str() with a more "Rivety" mixedCase name.
   template <typename T>
   inline string toString(const T& x) {
     return lexical_cast<string>(x);
   }
 
   /// Replace the first instance of patt with repl
   inline string& replace_first(string& str, const string& patt, const string& repl) {
     if (!contains(str, patt)) return str; //< contains from RivetSTL
     str.replace(str.find(patt), patt.size(), repl);
     return str;
   }
 
   /// @brief Replace all instances of patt with repl
   ///
   /// @note Finding is interleaved with replacement, so the second search happens after
   /// first replacement, etc. This could lead to infinite loops and other counterintuitive
   /// behaviours if not careful.
   inline string& replace_all(string& str, const string& patt, const string& repl) {
     if (!contains(str, patt)) return str; //< contains from RivetSTL
     while (true) {
       string::size_type it = str.find(patt);
       if (it == string::npos) break;
       str.replace(it, patt.size(), repl);
     }
     return str;
   }
 
 
   /// Case-insensitive string comparison function
   inline int nocase_cmp(const string& s1, const string& s2) {
     string::const_iterator it1 = s1.begin();
     string::const_iterator it2 = s2.begin();
     while ( (it1 != s1.end()) && (it2 != s2.end()) ) {
       if(::toupper(*it1) != ::toupper(*it2)) { // < Letters differ?
         // Return -1 to indicate smaller than, 1 otherwise
         return (::toupper(*it1) < ::toupper(*it2)) ? -1 : 1;
       }
       // Proceed to the next character in each string
       ++it1;
       ++it2;
     }
     size_t size1 = s1.size(), size2 = s2.size(); // Cache lengths
     // Return -1,0 or 1 according to strings' lengths
     if (size1 == size2) return 0;
     return (size1 < size2) ? -1 : 1;
   }
 
 
   /// Case-insensitive string equality function
   inline bool nocase_equals(const string& s1, const string& s2) {
     return nocase_cmp(s1, s2) == 0;
   }
 
 
   /// Convert a string to lower-case
   inline string toLower(const string& s) {
     string out = s;
     std::transform(out.begin(), out.end(), out.begin(), (int(*)(int)) std::tolower);
     return out;
   }
 
 
   /// Convert a string to upper-case
   inline string toUpper(const string& s) {
     string out = s;
     std::transform(out.begin(), out.end(), out.begin(), (int(*)(int)) std::toupper);
     return out;
   }
 
 
   /// Check whether a string @a start is found at the start of @a s
   inline bool startsWith(const string& s, const string& start) {
     if (s.length() < start.length()) return false;
     return s.substr(0, start.length()) == start;
   }
 
 
   /// Check whether a string @a end is found at the end of @a s
   inline bool endsWith(const string& s, const string& end) {
     if (s.length() < end.length()) return false;
     return s.substr(s.length() - end.length()) == end;
   }
 
 
   // Terminating version of strjoin, for empty fargs list
   inline string strcat() { return ""; }
   /// Make a string containing the concatenated string representations of each item in the variadic list
   template<typename T, typename... Ts>
   inline string strcat(T value, Ts... fargs) {
     const string strthis = lexical_cast<string>(value);
     const string strnext = strcat(fargs...);
     return strnext.empty() ? strthis : strthis + strnext;
   }
 
 
   /// Make a string containing the string representations of each item in v, separated by sep
   template <typename T>
   inline string join(const vector<T>& v, const string& sep=" ") {
     string rtn;
     for (size_t i = 0; i < v.size(); ++i) {
       if (i != 0) rtn += sep;
       rtn += to_str(v[i]);
     }
     return rtn;
   }
 
   /// Make a string containing the string representations of each item in v, separated by sep
   template <>
   inline string join(const vector<string>& v, const string& sep) {
     string rtn;
     for (size_t i = 0; i < v.size(); ++i) {
       if (i != 0) rtn += sep;
       rtn += v[i];
     }
     return rtn;
   }
 
   /// Make a string containing the string representations of each item in s, separated by sep
   template <typename T>
   inline string join(const set<T>& s, const string& sep=" ") {
     string rtn;
     for (const T& x : s) {
       if (rtn.size() > 0) rtn += sep;
       rtn += to_str(x);
     }
     return rtn;
   }
 
   /// Make a string containing the string representations of each item in s, separated by sep
   template <>
   inline string join(const set<string>& s, const string& sep) {
     string rtn;
     for (const string & x : s) {
       if (rtn.size() > 0) rtn += sep;
       rtn += x;
     }
     return rtn;
   }
 
   /// @brief Split a string on a specified separator string
   inline vector<string> split(const string& s, const string& sep) {
     vector<string> dirs;
     string tmp = s;
     while (true) {
       const size_t delim_pos = tmp.find(sep);
       if (delim_pos == string::npos) break;
       const string dir = tmp.substr(0, delim_pos);
       if (dir.length()) dirs.push_back(dir); // Don't insert "empties"
       tmp.replace(0, delim_pos+1, "");
     }
     if (tmp.length()) dirs.push_back(tmp); // Don't forget the trailing component!
     return dirs;
   }
 
   /// Left-pad the given string @a s to width @a width
   inline string lpad(const string& s, size_t width, const string& padchar=" ") {
     if (s.size() >= width) return s;
     return string(width - s.size(), padchar[0]) + s;
   }
 
   /// Right-pad the given string @a s to width @a width
   inline string rpad(const string& s, size_t width, const string& padchar=" ") {
     if (s.size() >= width) return s;
     return s + string(width - s.size(), padchar[0]);
   }
 
   /// @}
 
 
 
   /// @defgroup pathutils Path utils
   /// @{
 
   /// @brief Split a path string with colon delimiters
   ///
   /// Ignores zero-length substrings. Designed for getting elements of filesystem paths, naturally.
   inline vector<string> pathsplit(const string& path) {
     return split(path, ":");
   }
 
   /// @brief Join several filesystem paths together with the standard ':' delimiter
   ///
   /// Note that this does NOT join path elements together with a platform-portable
   /// directory delimiter, cf. the Python @c {os.path.join}!
   inline string pathjoin(const vector<string>& paths) {
     return join(paths, ":");
   }
 
   /// Operator for joining strings @a a and @a b with filesystem separators
   inline string operator / (const string& a, const string& b) {
     // Ensure that a doesn't end with a slash, and b doesn't start with one, to avoid "//"
     const string anorm = (a.find("/") != string::npos) ? a.substr(0, a.find_last_not_of("/")+1) : a;
     const string bnorm = (b.find("/") != string::npos) ? b.substr(b.find_first_not_of("/")) : b;
     return anorm + "/" + bnorm;
   }
 
   /// Get the basename (i.e. terminal file name) from a path @a p
   inline string basename(const string& p) {
     if (!contains(p, "/")) return p;
     return p.substr(p.rfind("/")+1);
   }
 
   /// Get the dirname (i.e. path to the penultimate directory) from a path @a p
   inline string dirname(const string& p) {
     if (!contains(p, "/")) return "";
     return p.substr(0, p.rfind("/"));
   }
 
   /// Get the stem (i.e. part without a file extension) from a filename @a f
   inline string file_stem(const string& f) {
     if (!contains(f, ".")) return f;
     return f.substr(0, f.rfind("."));
   }
 
   /// Get the file extension from a filename @a f
   inline string file_extn(const string& f) {
     if (!contains(f, ".")) return "";
     return f.substr(f.rfind(".")+1);
   }
 
   /// @}
 
 
 
   /// @defgroup contutils Container utils
   /// @{
 
   /// Return number of true elements in the container @a c .
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline unsigned int count(const CONTAINER& c) {
     // return std::count_if(std::begin(c), std::end(c), [](const typename CONTAINER::value_type& x){return bool(x);});
     unsigned int rtn = 0;
     for (const auto& x : c) if (bool(x)) rtn += 1;
     return rtn;
   }
 
   // /// Return number of elements in the container @a c for which @c f(x) is true.
   // template <typename CONTAINER>
   // inline unsigned int count(const CONTAINER& c, const std::function<bool(typename CONTAINER::value_type)>& f) {
   //   return std::count_if(std::begin(c), std::end(c), f);
   // }
 
   /// Return number of elements in the container @a c for which @c f(x) is true.
   template <typename CONTAINER, typename FN,
             //typename FN = bool(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline unsigned int count(const CONTAINER& c, const FN& f) {
     return std::count_if(std::begin(c), std::end(c), f);
   }
 
 
 
   /// Return true if x is true for any x in container c, otherwise false.
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool any(const CONTAINER& c) {
     // return std::any_of(std::begin(c), std::end(c), [](const auto& x){return bool(x);});
     for (const auto& x : c) if (bool(x)) return true;
     return false;
   }
 
   // /// Return true if f(x) is true for any x in container c, otherwise false.
   // template <typename CONTAINER>
   // inline bool any(const CONTAINER& c, const std::function<bool(typename CONTAINER::value_type)>& f) {
   //   return std::any_of(std::begin(c), std::end(c), f);
   // }
 
   /// Return true if f(x) is true for any x in container c, otherwise false.
   template <typename CONTAINER, typename FN,
             //typename FN = double(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool any(const CONTAINER& c, const FN& f) {
     return std::any_of(std::begin(c), std::end(c), f);
   }
 
 
 
   /// Return true if @a x is true for all @c x in container @a c, otherwise false.
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool all(const CONTAINER& c) {
     // return std::all_of(std::begin(c), std::end(c), [](const auto& x){return bool(x);});
     for (const auto& x : c) if (!bool(x)) return false;
     return true;
   }
 
   // /// Return true if @a f(x) is true for all @c x in container @a c, otherwise false.
   // template <typename CONTAINER>
   // inline bool all(const CONTAINER& c, const std::function<bool(typename CONTAINER::value_type)>& f) {
   //   return std::all_of(std::begin(c), std::end(c), f);
   // }
 
   /// Return true if @a f(x) is true for all @c x in container @a c, otherwise false.
   template <typename CONTAINER, typename FN,
             //typename FN = double(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool all(const CONTAINER& c, const FN& f) {
     return std::all_of(std::begin(c), std::end(c), f);
   }
 
 
   /// Return true if @a x is false for all @c x in container @a c, otherwise false.
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool none(const CONTAINER& c) {
     // return std::none_of(std::begin(c), std::end(c), [](){});
     for (const auto& x : c) if (bool(x)) return false;
     return true;
   }
 
   // /// Return true if @a f(x) is false for all @c x in container @a c, otherwise false.
   // template <typename C>
   // inline bool none(const C& c, const std::function<bool(typename C::value_type)>& f) {
   //   return std::none_of(std::begin(c), std::end(c), f);
   // }
 
   /// Return true if @a f(x) is false for all @c x in container @a c, otherwise false.
   template <typename CONTAINER, typename FN,
             //typename FN = double(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline bool none(const CONTAINER& c, const FN& f) {
     return std::none_of(std::begin(c), std::end(c), f);
   }
 
 
   // /// A single-container-arg version of std::transform, aka @c map
   // template <typename CONTAINER1, typename CONTAINER2>
   // inline const CONTAINER2& transform(const CONTAINER1& in, CONTAINER2& out,
   //                            const std::function<typename CONTAINER2::value_type(typename CONTAINER1::value_type)>& f) {
   //   out.clear(); out.resize(in.size());
   //   std::transform(in.begin(), in.end(), out.begin(), f);
   //   return out;
   // }
 
   /// A single-container-arg version of std::transform
   /// @todo Make the function template specific to ParticleBase
   /// or introduce C++20 concepts
   template <typename CONTAINER1, typename CONTAINER2,
             typename FN = typename std::decay_t<CONTAINER2>::value_type(
                           const typename std::decay_t<CONTAINER1>::value_type::ParticleBase&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER1>> &&
                                          is_citerable_v<std::decay_t<CONTAINER2>> >>
   inline const CONTAINER2& transform(const CONTAINER1& in, CONTAINER2& out, FN&& f) {
     out.clear(); out.resize(in.size());
     std::transform(in.begin(), in.end(), out.begin(), std::forward<FN>(f));
     return out;
   }
 
   /// A single-container-arg, return-value version of std::transform, aka @c map
   /// @todo Make the function template polymorphic... or specific to ParticleBase
   template <typename CONTAINER1, typename RTN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER1>> >>
   inline std::vector<RTN> transform(const CONTAINER1& in,
                                     const std::function<RTN(typename CONTAINER1::value_type::ParticleBase)>& f) {
     std::vector<RTN> out;
     transform(in, out, f);
     return out;
   }
 
   // /// A single-container-arg version of std::accumulate, aka @c reduce
   // template <typename CONTAINER1, typename T>
   // inline T accumulate(const CONTAINER1& in, const T& init, const std::function<T(typename CONTAINER1::value_type)>& f) {
   //   const T rtn = std::accumulate(in.begin(), in.end(), init, f);
   //   return rtn;
   // }
 
   /// A single-container-arg version of std::accumulate, aka @c reduce
   template <typename CONTAINER1, typename T, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER1>> >>
   inline T accumulate(const CONTAINER1& in, const T& init, const FN& f) {
     const T rtn = std::accumulate(in.begin(), in.end(), init, f);
     return rtn;
   }
 
 
   /// @brief Generic sum function, adding @c x for all @c x in container @a c
   ///
   /// @note Default-constructs the return type -- not always possible! Supply an explicit start value if necessary.
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline typename CONTAINER::value_type sum(const CONTAINER& c) {
     typename CONTAINER::value_type rtn; //< default construct return type
     for (const auto& x : c) rtn += x;
     return rtn;
   }
 
   /// Generic sum function, adding @c x for all @c x in container @a c, starting with @a start
   ///
   /// @note It's more more flexible here to not use CONTAINER::value_type, allowing implicit casting to T.
   template <typename CONTAINER, typename T,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline T sum(const CONTAINER& c, const T& start) {
     T rtn = start;
     for (const auto& x : c) rtn += x;
     return rtn;
   }
 
   /// Generic sum function, adding @a fn(@c x) for all @c x in container @a c, starting with @a start
   template <typename CONTAINER, typename T,
             typename FN = T(const typename std::decay_t<CONTAINER>::value_type&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline T sum(CONTAINER&& c, FN&& fn, const T& start=T()) {
     auto f = std::function(std::forward<FN>(fn));
     T rtn = start;
     for (const auto& x : c) rtn += fn(x);
     return rtn;
   }
 
 
   /// In-place generic sum function, adding @c x on to container @a out for all @c x in container @a c
   ///
   /// @note It's more more flexible here to not use CONTAINER::value_type, allowing implicit casting to T.
   template <typename CONTAINER, typename T,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline T& isum(const CONTAINER& c, T& out) {
     for (const auto& x : c) out += x;
     return out;
   }
 
   /// In-place generic sum function, adding @a fn(@c x) on to container @a out for all @c x in container @a c
   ///
   /// @note It's more more flexible here to not use CONTAINER::value_type, allowing implicit casting to T.
   template <typename CONTAINER, typename FN, typename T,
             //typename FN = double(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline T& isum(const CONTAINER& c, const FN& f, T& out) {
     for (const auto& x : c) out += f(x);
     return out;
   }
 
 
 
   /// Filter a collection in-place, removing the subset that passes the supplied function
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& idiscard(CONTAINER& c, const FN& f) {
     const auto newend = std::remove_if(std::begin(c), std::end(c), f);
     c.erase(newend, c.end());
     return c;
   }
 
   /// Version with element-equality comparison in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& idiscard(CONTAINER& c, const typename CONTAINER::value_type& y) {
     return idiscard(c, [&](typename CONTAINER::value_type& x){ return x == y; });
   }
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& idiscard_if_any(CONTAINER& c, const CONTAINER& ys) {
     return idiscard(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); });
   }
 
 
   /// Filter a collection by copy, removing the subset that passes the supplied function
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER discard(const CONTAINER& c, const FN& f) {
     CONTAINER rtn = c;
     return idiscard(rtn, f); ///< @todo More efficient would be copy_if with back_inserter...
   }
 
   /// Version with element-equality comparison in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER discard(const CONTAINER& c, const typename CONTAINER::value_type& y) {
     return discard(c, [&](typename CONTAINER::value_type& x){ return x == y; });
   }
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER discard_if_any(const CONTAINER& c, const CONTAINER& ys) {
     return discard(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); });
   }
 
 
   /// Filter a collection by copy into a supplied container, removing the subset that passes the supplied function
   ///
   /// @note New container will be replaced, not appended to
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             //typename FN = bool(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& discard(const CONTAINER& c, const FN& f, CONTAINER& out) {
     out = discard(c, f);
     return out;
   }
 
   /// Version with element-equality comparison in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& discard(const CONTAINER& c, const typename CONTAINER::value_type& y, CONTAINER& out) {
     return discard(c, [&](typename CONTAINER::value_type& x){ return x == y; }, out);
   }
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& discard_if_any(const CONTAINER& c, const CONTAINER& ys, CONTAINER& out) {
     return discard(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); }, out);
   }
 
 
 
   /// Filter a collection in-place, keeping the subset that passes the supplied function
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
       inline CONTAINER& iselect(CONTAINER& c, const FN& f) {
     auto invf = [&](const typename CONTAINER::value_type& x){ return !f(x); };
     return idiscard(c, invf); //< yes, intentional!
   }
 
   // No single equality-comparison version for select, since that would be silly!
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& iselect_if_any(CONTAINER& c, const CONTAINER& ys) {
     return iselect(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); });
   }
 
 
   /// Filter a collection by copy, keeping the subset that passes the supplied function
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER select(const CONTAINER& c, const FN& f) {
     CONTAINER rtn = c;
     return iselect(rtn, f); ///< @todo More efficient would be copy_if with back_inserter ... but is that equally container agnostic?
   }
 
   // No single equality-comparison version for select, since that would be silly!
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER select_if_any(const CONTAINER& c, const CONTAINER& ys) {
     return select(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); });
   }
 
 
   /// Filter a collection by copy into a supplied container, keeping the subset that passes the supplied function
   ///
   /// @note New container will be replaced, not appended to
   ///
   /// @todo Use const std::function<bool(typename CONTAINER::value_type)>... but need polymorphism for ParticleBase
   template <typename CONTAINER, typename FN,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& select(const CONTAINER& c, const FN& f, CONTAINER& out) {
     out = select(c, f);
     return out;
   }
 
   // No single equality-comparison version for select, since that would be silly!
 
   /// Version with several element-equality comparisons in place of a function
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER& select_if_any(const CONTAINER& c, const CONTAINER& ys, CONTAINER& out) {
     return select(c, [&](typename CONTAINER::value_type& x){ return contains(ys, x); }, out);
   }
 
 
 
   /// @brief Slice of the container elements cf. Python's [i:j] syntax
   ///
   /// The element at the @a j index is not included in the returned container.
   /// @a i and @a j can be negative, treated as backward offsets from the end of the container.
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER slice(const CONTAINER& c, int i, int j) {
     CONTAINER rtn;
     const size_t off1 = (i >= 0) ? i : c.size() + i;
     const size_t off2 = (j >= 0) ? j : c.size() + j;
     if (off1 > c.size() || off2 > c.size()) throw RangeError("Attempting to slice beyond requested offsets");
     if (off2 < off1) throw RangeError("Requested offsets in invalid order");
     rtn.resize(off2 - off1);
     std::copy(c.begin()+off1, c.begin()+off2, rtn.begin());
     return rtn;
   }
 
   /// @brief Tail slice of the container elements cf. Python's [i:] syntax
   ///
   /// Single-index specialisation of @c slice(c, i, j)
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER slice(const CONTAINER& c, int i) {
     return slice(c, i, c.size());
   }
 
   /// @brief Head slice of the @a n first container elements
   ///
   /// Negative @a n means to take the head excluding the @a n -element tail
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER head(const CONTAINER& c, int n) {
     // if (n > c.size()) throw RangeError("Requested head longer than container");
     if (n < 0) n = std::max(0, (int)c.size()+n);
     n = std::min(n, (int)c.size());
     return slice(c, 0, n);
   }
 
   /// @brief Tail slice of the @a n last container elements
   ///
   /// Negative @a n means to take the tail from after the @a n th element
   template <typename CONTAINER,
             typename = std::enable_if_t< is_citerable_v<std::decay_t<CONTAINER>> >>
   inline CONTAINER tail(const CONTAINER& c, int n) {
     // if (n > c.size()) throw RangeError("Requested tail longer than container");
     if (n < 0) n = std::max(0, (int)c.size()+n);
     n = std::min(n, (int)c.size());
     return slice(c, c.size()-n);
   }
 
 
   using std::min;
   using std::max;
 
   /// Find the minimum value in the vector
   inline double min(const vector<double>& in, double errval=DBL_NAN) {
     const auto e = std::min_element(in.begin(), in.end());
     return e != in.end() ? *e : errval;
   }
 
   /// Find the maximum value in the vector
   inline double max(const vector<double>& in, double errval=DBL_NAN) {
     const auto e = std::max_element(in.begin(), in.end());
     return e != in.end() ? *e : errval;
   }
 
   /// Find the minimum and maximum values in the vector
   inline pair<double,double> minmax(const vector<double>& in, double errval=DBL_NAN) {
     const auto e = std::minmax_element(in.begin(), in.end());
     const double rtnmin = e.first != in.end() ? *e.first : errval;
     const double rtnmax = e.second != in.end() ? *e.first : errval;
     return std::make_pair(rtnmin, rtnmax);
   }
 
 
   /// Find the minimum value in the vector
   inline int min(const vector<int>& in, int errval=-1) {
     const auto e = std::min_element(in.begin(), in.end());
     return e != in.end() ? *e : errval;
   }
 
   /// Find the maximum value in the vector
   inline int max(const vector<int>& in, int errval=-1) {
     const auto e = std::max_element(in.begin(), in.end());
     return e != in.end() ? *e : errval;
   }
 
   /// Find the minimum and maximum values in the vector
   inline pair<int,int> minmax(const vector<int>& in, int errval=-1) {
     const auto e = std::minmax_element(in.begin(), in.end());
     const double rtnmin = e.first != in.end() ? *e.first : errval;
     const double rtnmax = e.second != in.end() ? *e.first : errval;
     return std::make_pair(rtnmin, rtnmax);
   }
 
   /// @}
 
 
   /// @defgroup contcombutils Container-combinatorics utils
   /// @{
 
   /// @brief Return the index from a vector which best matches fn(c[i]) to the target value
   ///
   /// A NaN return from the function will be counted as a no-match, as will combinations giving
   /// a value outside the given @a minval .. @a maxval range. A -1 index is returned in the
   /// case that no valid match is found.
   template <typename CONTAINER,
             typename FN = double(const typename std::decay_t<CONTAINER>::value_type&),
             typename = isCIterable<CONTAINER>>
   inline int closestMatchIndex(CONTAINER&& c, FN&& fn,
                    double target, double minval=-DBL_MAX, double maxval=DBL_MAX) {
     auto f = std::function(std::forward<FN>(fn));
     int ibest = -1;
     double best = DBL_NAN;
     for (size_t i = 0; i < c.size(); ++i) {
       const double val = f(c[i]);
       if (isnan(val)) continue;
       if (val < minval || val > maxval) continue;
       if (isnan(best) || fabs(val-target) < fabs(best-target)) {
         best = val;
         ibest = i;
       }
     }
     return ibest;
   }
 
   /// @brief Return the indices from two vectors which best match fn(c1[i], c2[j]) to the target value
   ///
   /// A NaN return from the function will be counted as a no-match, as will combinations giving
   /// a value outside the given @a minval .. @a maxval range. A {-1,-1} pair is returned in the
   /// case that no valid match is found.
   ///
   /// @note No attempt is made to avoid duplication: the input lists are assumed independent and
   ///   the user should check the sanity of the result, e.g. c1[i] and c2[j] are not the same object.
   template <typename CONTAINER1, typename CONTAINER2,
             typename FN = double(const typename std::decay_t<CONTAINER1>::value_type&,
                                  const typename std::decay_t<CONTAINER2>::value_type&),
             typename = isCIterable<CONTAINER1, CONTAINER2>>
   inline pair<int,int> closestMatchIndices(CONTAINER1&& c1, CONTAINER2&& c2, FN&& fn,
                        double target, double minval=-DBL_MAX, double maxval=DBL_MAX) {
     auto f = std::function(std::forward<FN>(fn));
     pair<int,int> ijbest{-1,-1};
     double best = DBL_NAN;
     for (size_t i = 0; i < c1.size(); ++i) {
       for (size_t j = 0; j < c2.size(); ++j) {
         const double val = f(c1[i], c2[j]);
         if (isnan(val)) continue;
         if (val < minval || val > maxval) continue;
         if (isnan(best) || fabs(val-target) < fabs(best-target)) {
           best = val;
           ijbest = {i,j};
         }
       }
     }
     return ijbest;
   }
 
   /// @brief Return the index from a vector which best matches fn(c[i], x) to the target value
   ///
   /// A NaN return from the function will be counted as a no-match, as will combinations giving
   /// a value outside the given @a minval .. @a maxval range. A -1 index is returned in the
   /// case that no valid match is found.
   ///
   /// @note No attempt is made to avoid duplication: the inputs are assumed independent and
   ///   the user should check the sanity of the result, e.g. c[i] and x are not the same object.
   template <typename CONTAINER, typename T,
             typename FN = double(const typename std::decay_t<CONTAINER>::value_type&, const std::decay_t<T>&),
             typename = isCIterable<CONTAINER>>
   inline int closestMatchIndex(CONTAINER&& c, const T& x, FN&& fn,
                    double target, double minval=-DBL_MAX, double maxval=DBL_MAX) {
     pair<int,int> ijbest = closestMatchIndices(std::forward<CONTAINER>(c), vector<T>{x}, std::forward<FN>(fn), target, minval, maxval);
     return ijbest.first;
   }
 
   /// @brief Return the index from a vector which best matches fn(x, c[j]) to the target value
   ///
   /// A NaN return from the function will be counted as a no-match, as will combinations giving
   /// a value outside the given @a minval .. @a maxval range. A -1 index is returned in the
   /// case that no valid match is found.
   ///
   /// @note No attempt is made to avoid duplication: the inputs are assumed independent and
   ///   the user should check the sanity of the result, e.g. c[i] and x are not the same object.
   template <typename CONTAINER, typename T, typename FN, typename = isCIterable<CONTAINER>>
   inline int closestMatchIndex(T&& x, CONTAINER&& c, FN&& fn,
                    double target, double minval=-DBL_MAX, double maxval=DBL_MAX) {
     return closestMatchIndex(std::forward<CONTAINER>(c), std::forward<T>(x), std::forward<FN>(fn), target, minval, maxval);
   }
 
   /// @}
 
 
   /// @brief Get a parameter from a named environment variable, with automatic type conversion
   ///
   /// @note Return @a fallback if the variable is not defined, otherwise convert its string to the template type
   /// @todo Should the param name have to be specific to an analysis? Can specialise as an Analysis member fn.
   /// @ingroup utils
   template <typename T>
   T getEnvParam(const std::string name, const T& fallback) {
     char* env = getenv(name.c_str());
     return env ? lexical_cast<T>(env) : fallback;
   }
 
 
 
   /// @brief Get the contents of a vector between two indices
   ///
   /// @ingroup utils
   template<class T>
   vector<T> slice(const vector<T>& v, int startidx, int endidx) {
 
     if (startidx < 0 || endidx <= startidx || endidx >= v.size())
       throw RangeError("Requested start or end indices incompatible with given vector");
 
     auto start = v.begin() + startidx;
     auto end = v.begin() + endidx;
 
     vector<T> output(endidx - startidx);
 
     copy(start, end, output.begin());
 
     return output;
   }
 
 
 }
 
 #endif

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