Dg_and_Dg.hpp

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/* Subtracts a Dg from a Dg, yielding a
   Tensor3_antisymmetric. */
 
#pragma once
 
namespace FTensor
{
  /* A(i,j,k)-B(i,k,j)->Tensor3_antisymmetric */
 
  template <class A, class B, class T, class U, int Dim, char i, char j, char k>
  class Dg_and_Dg_12
  {
    Dg_Expr<A, T, Dim, Dim, i, j, k> iterA;
    Dg_Expr<B, U, Dim, Dim, i, k, j> iterB;
 
  public:
    typename promote<T, U>::V
    operator()(const int N1, const int N2, const int N3) const
    {
      return iterA(N1, N2, N3) - iterB(N1, N3, N2);
    }
 
    Dg_and_Dg_12(const Dg_Expr<A, T, Dim, Dim, i, j, k> &a,
                 const Dg_Expr<B, U, Dim, Dim, i, k, j> &b)
        : iterA(a), iterB(b)
    {}
  };
 
  template <class A, class B, class T, class U, int Dim, char i, char j, char k>
  Tensor3_antisymmetric_Expr<Dg_and_Dg_12<A, B, T, U, Dim, i, j, k>,
                             typename promote<T, U>::V, Dim, Dim, i, j, k>
  operator&&(const Dg_Expr<A, T, Dim, Dim, i, j, k> &a,
             const Dg_Expr<B, U, Dim, Dim, i, k, j> &b)
  {
    using TensorExpr = Dg_and_Dg_12<A, B, T, U, Dim, i, j, k>;
    return Tensor3_antisymmetric_Expr<TensorExpr, typename promote<T, U>::V,
                                      Dim, Dim, i, j, k>(TensorExpr(a, b));
  }
 
  /* A(i,j,k)-B(k,j,i)->Tensor3_antisymmetric */
  /* We have to do a little index gymnastics here because a
     Tensor3_antisymmetric is antisymmetric on the last two indices, not
     the first and last index. */
 
  template <class A, class B, class T, class U, int Dim, char i, char j, char k>
  class Dg_and_Dg_02
  {
    Dg_Expr<A, T, Dim, Dim, i, j, k> iterA;
    Dg_Expr<B, U, Dim, Dim, k, j, i> iterB;
 
  public:
    typename promote<T, U>::V
    operator()(const int N1, const int N2, const int N3) const
    {
      return iterA(N2, N1, N3) - iterB(N3, N1, N2);
    }
 
    Dg_and_Dg_02(const Dg_Expr<A, T, Dim, Dim, i, j, k> &a,
                 const Dg_Expr<B, U, Dim, Dim, k, j, i> &b)
        : iterA(a), iterB(b)
    {}
  };
 
  template <class A, class B, class T, class U, int Dim, char i, char j, char k>
  Tensor3_antisymmetric_Expr<Dg_and_Dg_02<A, B, T, U, Dim, i, j, k>,
                             typename promote<T, U>::V, Dim, Dim, j, i, k>
  operator&&(const Dg_Expr<A, T, Dim, Dim, i, j, k> &a,
             const Dg_Expr<B, U, Dim, Dim, k, j, i> &b)
  {
    using TensorExpr = Dg_and_Dg_02<A, B, T, U, Dim, i, j, k>;
    return Tensor3_antisymmetric_Expr<TensorExpr, typename promote<T, U>::V,
                                      Dim, Dim, j, i, k>(TensorExpr(a, b));
  }
}