Combinatorics.h

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//# $Id$

#ifndef SCIMATH_COMBINATORICS_H
#define SCIMATH_COMBINATORICS_H


//# Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/Arrays/Vector.h>
#include <casacore/casa/OS/Mutex.h>

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)
  {
    //# This test is thread-safe.
    if (n >= _factorialCacheSize) 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 Mutex theirMutex;
};
} //# NAMESPACE CASACORE - END

#endif