/*
    DFT++ is a density functional package developed by the research group
    of Professor Tomas Arias

    Copyright 1996-2003 Sohrab Ismail-Beigi

    This file is part of DFT++.

    DFT++ is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    DFT++ is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with DFT++; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Please see the file CREDITS for a list of authors.

    For academic users, we request that publications using results obtained with
    this software reference

    "New algebraic formulation of density functional calculation," by Sohrab Ismail-Beigi
    and T.A. Arias, Computer Physics Communications 128:1-2, 1-45 (June 2000).

    and, if using the wavelet basis, further reference

    "Multiresolution analysis of electronic structure: semicardinal and wavelet bases,"
    T.A. Arias, Reviews of Modern Physics 71:1, 267-311 (January 1999).

    and 

    "Robust ab initio calculation of condensed matter: transparent convergence through
    semicardinal multiresolution analysis,'' I.P. Daykov, T.A. Arias, and
    Torkel D. Engeness, Physical Review Letters, 90:21, 216402 (May 2003).

    For your convenience, preprints of the above articles may be obtained from
    http://arXiv.org/abs/cond-mat/9909130, 9805262, and 0204411, respectively.
*/

/*
 *     Sohrab Ismail-Beigi           Mar. 30, 1997
 *
 * Solve the Poisson equation.
 *
 */

/* $Id: poisson.cpp,v 1.5.2.9 2003/05/29 18:54:32 ivan Exp $ */

#include "header.h"

/*
 * Solve poisson equation...trivial for a planewave basis!
 *
 *     d = -4*pi*invL(Obar(J(n))).
 */
void solve_poisson(RealSpaceScalarFieldColumn &density, 
	      CoeffSpaceScalarFieldColumn &potential)
{
#ifdef DFT_PROFILING
  timerOn(17);   // Turn on solve_poisson timer
#endif // DFT_PROFILING

  const real pi = M_PI;

  //  potential = (-4.0*pi)*invL(Obar(J(density)));
  // the code below saves on temporaries
  apply_J(density, potential);
  apply_Obar(potential, potential);
  apply_invL(potential, potential);
  potential*=(-4*pi);
  
  
#ifdef DFT_PROFILING
  timerOff(17);   // Turn off solve_poisson timer
#endif // DFT_PROFILING
}