codac2_max.h

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#pragma once
 
#include "codac2_Interval.h"
#include "codac2_AnalyticType.h"
#include "codac2_AnalyticExprWrapper.h"
 
namespace codac2
{
  struct MaxOp
  {
    template<typename X1,typename X2>
    static std::string str(const X1& x1, const X2& x2)
    {
      return "max(" + x1->str() + "," + x2->str() + ")";
    }
 
    template<typename X1, typename X2>
    static std::pair<Index,Index> output_shape([[maybe_unused]] const X1& s1, [[maybe_unused]] const X2& s2)
    {
      return {1,1};
    }
 
    static Interval fwd(const Interval& x1, const Interval& x2);
    static ScalarType fwd_natural(const ScalarType& x1, const ScalarType& x2);
    static ScalarType fwd_centered(const ScalarType& x1, const ScalarType& x2);
    static void bwd(const Interval& y, Interval& x1, Interval& x2);
  };
 
  // Analytic operator
  // The following function can be used to build analytic expressions.
 
  inline ScalarExpr
  max(const ScalarExpr& x1, const ScalarExpr& x2)
  {
    return { std::make_shared<AnalyticOperationExpr<MaxOp,ScalarType,ScalarType,ScalarType>>(x1,x2) };
  }
 
  inline ScalarType MaxOp::fwd_natural(const ScalarType& x1, const ScalarType& x2)
  {
    return {
      fwd(x1.a, x2.a),
      x1.def_domain && x2.def_domain
    };
  }
 
  inline ScalarType MaxOp::fwd_centered(const ScalarType& x1, const ScalarType& x2)
  {
    if(centered_form_not_available_for_args(x1,x2))
      return fwd_natural(x1,x2);
    
    assert(x1.da.rows() == 1);
    assert(x1.da.rows() == x2.da.rows() && x1.da.cols() == x2.da.cols());
 
    IntervalMatrix d(1,x1.da.cols());
    for(Index i = 0 ; i < d.size() ; i++)
      d(0,i) = chi(x1.a-x2.a, x2.da(0,i), x1.da(0,i));
 
    return {
      fwd(x1.m, x2.m),
      fwd(x1.a, x2.a),
      d,
      x1.def_domain && x2.def_domain
        && (x1.a != x2.a) // def domain of the derivative of max
    };
  }
 
  // Inline functions
 
  inline Interval MaxOp::fwd(const Interval& x1, const Interval& x2)
  {
    return max(x1,x2);
  }
 
  inline void MaxOp::bwd(const Interval& y, Interval& x1, Interval& x2)
  {
    // The content of this function comes from the IBEX library.
    // See ibex::Interval (IBEX lib, main author: Gilles Chabert)
    //   https://ibex-lib.readthedocs.io
 
    if(y.is_empty())
    {
      x1.set_empty();
      x2.set_empty();
    }
 
    // Disjoint intervals
    else if(x2.lb() > x1.ub() || y.lb() > x1.ub())
    {
      // Then, max(x,x2) is necessarily x2
      if((x2 &= y).is_empty())
        x1.set_empty();
    }
 
    else if(x1.lb() > x2.ub() || y.lb() > x2.ub())
    {
      if((x1 &= y).is_empty())
        x2.set_empty();
    }
 
    else if(y.ub() < x1.lb() || y.ub() < x2.lb())
    {
      x1.set_empty();
      x2.set_empty();
    }
 
    else
    {
      // At this point, x1, x2 and y all mutually intersect
 
      if(x1.ub() > y.ub())
        x1 = Interval(x1.lb(),y.ub());
 
      if(x2.ub() > y.ub())
        x2 = Interval(x2.lb(),y.ub());
    }
  }
}