/**********************************************************

This software is part of J.-S. Caux's ABACUS library.

Copyright (c).

-----------------------------------------------------------

File:  NRG_K_Weight_integrand.cc

Purpose:  for NRG, this function specifies the momentum-dependent
          part of the perturbation prefactor.
          Collaboration with Robert Konik.

***********************************************************/
#include "JSC.h"

using namespace std;
using namespace JSC;

namespace JSC {

  // This function defines the integrand for momentum-dependent perturbation prefactor
  DP K_Weight_integrand (Vect_DP args)
  {
    // Momentum-dependent part of weight used in selecting kept form factors.
    // This function gives the integrand, with the weight being
    // \int_{-1/2}^{1/2} dx integrand(x)

    DP value;

    { // Case of a harmonic trap of strength omega_trap centered on 0:

      // args[0] == x
      // args[1] == iK
      // args[2] == L
      // args[3] == omega_trap

      value = 12.0 * args[0] * args[0] * cos(twoPI * args[0] * args[1]) * pow(args[2], 2.0) * pow(args[3], 3.0);
    }

    return(value);
  }



} // namespace JSC