BinomialCoefficients.h

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#ifndef _utl_BinomialCache_h_
#define _utl_BinomialCache_h_

#include <vector>
#include <utl/Singleton.h>


namespace utl {

  class BinomialCoefficients : public Singleton<BinomialCoefficients> {
  public:
    BinomialCoefficients(const int initialN = 3)
      : fMaxN(0), fCoefficients(1, 1) { Generate(initialN); }

    double
    operator()(const int n, const int k)
    {
      if (k < 0 || k > n)
        return 0;
      if (n > fMaxN)
        Generate(n);
      return GetUnchecked(n, k);
    }

  private:
    double& GetUnchecked(const int n, const int k)
    { return fCoefficients[n*(n+1)/2 + k]; }

    void Generate(const int n);

    int fMaxN;
    std::vector<double> fCoefficients;
  };

}


#endif