Combinatorics.h

Go to the documentation of this file.

// # Smooth.h: smooth vectors and arrays
// # Copyright (C) 2010 by ESO (in the framework of the ALMA collaboration)
// # Copyright (C) 1996,1997,1998,1999,2000,2001
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 of the License, or (at your
// # option) any later version.
// #
// # This library is distributed in the hope that it will be useful, but WITHOUT
// # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef SCIMATH_COMBINATORICS_H
#define SCIMATH_COMBINATORICS_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/Arrays/Vector.h>
 
#include <mutex>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary>
// Combinatorics related functions.
// </summary>
 
// <use visibility=export>
 
// # <author>Dave Mehringer</author>
//  <reviewed reviewer="" date="yyyy/mm/dd" tests="" demos="">
//  </reviewed>
 
// <prerequisite>
//   <li> <linkto class="Vector">Vector</linkto>
//   <li> <linkto class="Array">Array</linkto>
// </prerequisite>
 
// <etymology>
// self-explanatory
// </etymology>
 
// <synopsis>
// Various factorial and combinatorical functions.
// </synopsis>
 
// <motivation>
// Binomial coefficients needed for Images/ImageProfileFitter
// </motivation>
 
class Combinatorics {
 public:
  // Get n!
  static uInt factorial(const uInt n) {
    fillCache(n);
    return _factorialCache[n];
  }
 
  // "n choose k" = n!/(k!(n-k)!)
  // Exception is thrown if k > n.
  static uInt choose(const uInt n, const uInt k);
 
 private:
  static void fillCache(const uInt n);
 
  static Vector<uInt> _factorialCache;
  static volatile uInt _factorialCacheSize;  // # volatile for double checked lock
  static std::mutex theirMutex;
};
}  // namespace casacore
 
#endif