#ifndef BIVECTOR_H
#define BIVECTOR_H

// Definitions for generalized BiVector class
// $Id: BiVector.h,v 1.13 2002/10/22 17:07:58 sachs Exp $
// David Sachs - Fermilab - April 2002

// A BiVector is a 2xn (or nx2) matrix, which is implemented
// as a pair of vectors

#include <iostream>
#include <string>
#include <vector>

namespace CovMatrices
{
  class CovMatrix;

  // BiVector Class
  class BiVector
  {
    private:
    int n;	// order of BiVector
    std::vector<double> v0;
    std::vector<double> v1;

    public:
    friend class CovMatrix;

    //  *** Constructors ***

    // Construct Empty  or zero BiVector (Default Constructor)
    explicit inline BiVector(int m = 0) : n(m), v0(m), v1(m) {}

    // Copy Constructor (Uses Compiler generated version)

    // Construct from 2 Vectors
    BiVector(const std::vector<double>&, const std::vector<double>&);

    // Construct from Vector containing all 2*n elements
    explicit BiVector(const std::vector<double>&);

    // Destructor (Uses Compiler generated version)

    // Assignment functions

    // Copy Assignment (Uses Compiler generated version)

    // Assign from Vector containing all 2*n elements
    BiVector& operator=(const std::vector<double>&);

    // Get order
    int size() const {return n;}	// returns order

    // Set order without specific element initialization
    void resize(int);

    // Subscripting (any nonzero value is treated as 1)
    std::vector<double>& operator[] (int i)
    { return  (i ? v1 : v0); }

    const std::vector<double>& operator[] (int i) const
    { return  (i ? v1 : v0); }

    // Dump BiVector to vector<double>
    void dump(std::vector<double>&) const;

    // Print BiVector
    void put(std::ostream&) const;

    // Static function to display a vector<double>
    // This function is provided for BiVector and CovMatrix classes
    // because vector<double> does not have output operator defined
    static void printv( std::ostream&, const std::vector<double>& );

    // friend functions
    friend BiVector operator* (const CovMatrix&, const BiVector&);
    friend BiVector operator* (const BiVector&, const CovMatrix&);
  };

  // Declarations of non-member functions
  inline std::ostream& operator<<(std::ostream& o, const BiVector& B)
    { B.put(o); return o; }

 }  // namespace CovMatrices
#endif