message: Made Gradient_DDI also switch via DDI_Method enum. And renamed Gradient_DDI_direct to Gradient_DDI_Direct.
diff: @@ -123,7 +123,8 @@ namespace Engine
  void Gradient_DMI(const vectorfield & spins, vectorfield & gradient);
  // Calculates the Dipole-Dipole contribution to the effective field of spin ispin within system s
  void Gradient_DDI(const vectorfield& spins, vectorfield & gradient);
  - void Gradient_DDI_direct(const vectorfield& spins, vectorfield & gradient);
  + void Gradient_DDI_Cutoff(const vectorfield& spins, vectorfield & gradient);
  + void Gradient_DDI_Direct(const vectorfield& spins, vectorfield & gradient);
  void Gradient_DDI_FFT(const vectorfield& spins, vectorfield & gradient);
  // Quadruplet
  