homography.hpp

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/*******************************************************************
 *   This file is part of the source code of realroot kernel.
 *   Author(s): B. Mourrain, GALAAD, INRIA
 *              A. Mantzaflaris, GALAAD, INRIA
 ********************************************************************/
#ifndef realroot_homography_hpp
#define realroot_homography_hpp
//====================================================================

#include <realroot/Interval.hpp>

namespace mmx {

  // (ax + b)/(cx + d)
  template<class real>  struct homography
  {
    real a,b,c,d;
    
    homography(): a(1),b(0),c(0),d(1) {}
    homography(const homography& H): a(H.a),b(H.b),c(H.c),d(H.d) {}
    homography(const real& A, const real& B, const real& C, const real&D): a(A),b(B),c(C),d(D) {}
    
    void shift_hom     (const real & t ) {  b+=t*a; d+=t*c; }
    
    //  reciprocal_hom: t currently unused
    void reciprocal_hom(const real & t ) 
      { std::swap(a,b); std::swap(c,d); }
    
    void contract_hom  (const real & t ) { a*=t; c*=t; }
  };
  
  // multivariate homography
  template<class real>  struct homography_mv
  {
    Seq<homography<real> >  H;  
    
    homography_mv() { H << homography<real>(); }
    homography_mv(int n) {
      for (int i=0;i<n;++i ) H << homography<real>(); 
    }
    homography_mv(const real& A, const real& B, const real& C, const real&D)
      { 
        H << homography<real>(A,B,C,D); 
      }
    
    homography<real> operator[](int  i)     { return H[i]; }
    homography<real> operator[](unsigned & i){ return H[i]; }
    
    void shift_hom     (const real & t, const int & v) {  H[v].shift_hom(t); }
    void reciprocal_hom (const real & t, const int & v) { H[v].reciprocal_hom(t); }
    void contract_hom (const real & t, const int & v) { H[v].contract_hom(t); }
    void colapse () {for (unsigned j=0;j<H.size();j++) {
        H[j].a=H[j].b;
        H[j].c=H[j].d;
      }
    }
    int size() {return H.size();}
  };
  
}
//====================================================================
#endif  //realroot_homography_hpp