/*******************************************************************************
*
* McStas, neutron ray-tracing package
*         Copyright 1997-2002, All rights reserved
*         Risoe National Laboratory, Roskilde, Denmark
*         Institut Laue Langevin, Grenoble, France
*
* Component: Source_div
*
* %I
* Written by: KL
* Date: November 20, 1998
* Modified by: KL, 8 October 2001
* Version: $Revision: 1.22 $
* Origin: Risoe
* Release: McStas 1.6
*
* Neutron source with Gaussian or uniform divergence
*
* %D
* The routine is a rectangular neutron source, which has a gaussian or uniform
* divergent output in the forward direction.
* The neutron energy is uniformly distributed between E0-dE and E0+dE or
* a wavelength is uniformly distributed between Lambda0-dLambda and Lambda0+dLambda.
* If energy and wavelength are given, energy is used.
* In the case of uniform distribution (gauss=0), angles are uniformly distributed
* between -hdiv and +hdiv as well as -vdiv and +vdiv. For Gaussian distribution
* (gauss=1), 'hdiv' and 'vdiv' define the FWHM of a Gauss'schen distribution,
*
* Example: Source_div(width=0.1, height=0.1, hdiv=2, vdiv=2, E0=14, dE=2, gauss=0)
*
* %VALIDATION
* Feb 2005: tested by Kim Lefmann    (o.k.)
* Apr 2005: energy distribution used in external tests of Fermi choppers (o.k.)
* Jun 2005: wavelength distribution used in external tests of velocity selectors (o.k.)
* Validated by: K. Lieutenant
*
* %BUGS
* distribution is uniform in (hor. and vert.) angle (relative to moderator normal),
* therefore not suited for large angles
*
* %P
* width:    (m)  Width of source
* height:   (m)  Height of source
* hdiv:    (deg) FWHM (Gaussian) or maximal (uniform) horizontal divergence
* vdiv:    (deg) FWHM (Gaussian) or maximal (uniform) vertical divergence
* E0:      (meV) Mean energy of neutrons.
* dE:      (meV) Energy spread of neutrons.
* Lambda0: (Ang) Mean wavelength of neutrons (only relevant for E0=0)
* dLambda: (Ang) Wavelength spread of neutrons.
* gauss:    (-)  Criterion: 0: uniform, 1: Gaussian distribution (default)
*
* OUTPUT PARAMETERS:
* sigmah:  (rad) parameter 'sigma' of the Gaussian distribution for horizontal divergence
* sigmav:  (rad) parameter 'sigma' of the Gaussian distribution for vertical divergence
* p_init:   (-)  normalisation factor 1/'neutron_count'
*
* %E
*******************************************************************************/

DEFINE COMPONENT Source_div
DEFINITION PARAMETERS ()
SETTING PARAMETERS (width, height, hdiv, vdiv, E0=0.0, dE=0.0, Lambda0=0.0, dLambda=0.0, gauss=1)
OUTPUT PARAMETERS (sigmah, sigmav, p_init)
STATE PARAMETERS (x,y,z,vx,vy,vz,t,s1,s2,p)
DECLARE
%{
  double thetah, thetav, sigmah, sigmav, tan_h, tan_v, p_init;
%}
INITIALIZE
%{
  sigmah = DEG2RAD*hdiv/(2.0*sqrt(2.0*log(2.0)));
  sigmav = DEG2RAD*vdiv/(2.0*sqrt(2.0*log(2.0)));
  p_init = 1.0/mcget_ncount();

  if (width < 0 || height < 0 || hdiv < 0 || vdiv < 0
    || (!Lambda0 && !dLambda && (E0 <= 0 || dE < 0 || E0-dE <= 0))
    || (!E0 && !dE && (Lambda0 <= 0 || dLambda < 0 || Lambda0-dLambda <= 0))) {
      printf("Source_div: %s: Error in input parameter values!\n"
             "ERROR          Exiting\n",
           NAME_CURRENT_COMP);
      exit(0);
  }
%}
TRACE
%{
 double E,lambda,v;

 p=p_init;
 z=0;
 t=0;

 x=randpm1()*width/2.0;
 y=randpm1()*height/2.0;

 if (E0 > 0.0 && E0 > fabs(dE))
 { E=E0+dE*randpm1();                    /* Assume linear distribution */
   v=sqrt(E)*SE2V;
 }
 else if (Lambda0 > 0.0 && Lambda0 > fabs(dLambda))
 { lambda = Lambda0+dLambda*randpm1();   /* Assume linear distribution */
   v      = 3956.036 / lambda;
 }
 else
 { printf ("wrong energy and wavelength parameters in 'Source_div'");
   exit(-1);
 }

 if (gauss==1)
 { thetah = randnorm()*sigmah;
   thetav = randnorm()*sigmav;
 }
 else
 { thetah = randpm1()*hdiv*DEG2RAD;
   thetav = randpm1()*vdiv*DEG2RAD;
 }

 tan_h = tan(thetah);
 tan_v = tan(thetav);

 /* Perform the correct treatment - no small angle approx. here! */
 vz = v / sqrt(1 + tan_v*tan_v + tan_h*tan_h);
 vy = tan_v * vz;
 vx = tan_h * vz;
%}

MCDISPLAY
%{
  magnify("xy");
  multiline(5, -width/2.0, -height/2.0, 0.0,
                width/2.0, -height/2.0, 0.0,
                width/2.0,  height/2.0, 0.0,
               -width/2.0,  height/2.0, 0.0,
               -width/2.0, -height/2.0, 0.0);
%}

END
