source: sasview/sansmodels/src/c_models/lamellar.cpp @ 08648c0

/**
        This software was developed by the University of Tennessee as part of the
        Distributed Data Analysis of Neutron Scattering Experiments (DANSE)
        project funded by the US National Science Foundation.

        If you use DANSE applications to do scientific research that leads to
        publication, we ask that you acknowledge the use of the software with the
        following sentence:

        "This work benefited from DANSE software developed under NSF award DMR-0520547."

        copyright 2008, University of Tennessee
 */

/**
 * Scattering model classes
 * The classes use the IGOR library found in
 *   sansmodels/src/libigor
 *
 */

#include <math.h>
#include "parameters.hh"
#include <stdio.h>
using namespace std;
#include "lamellar.h"

/*  LamellarFFX  :  calculates the form factor of a lamellar structure - no S(q) effects included
            -NO polydispersion included
*/
static double lamellar_kernel(double dp[], double q){
  double scale,del,sld_bi,sld_sol,contr,bkg;    //local variables of coefficient wave
  double inten, qval,Pq;
  double Pi;


  Pi = 4.0*atan(1.0);
  scale = dp[0];
  del = dp[1];
  sld_bi = dp[2];
  sld_sol = dp[3];
  bkg = dp[4];
  qval = q;
  contr = sld_bi -sld_sol;

  Pq = 2.0*contr*contr/qval/qval*(1.0-cos(qval*del));

  inten = 2.0*Pi*scale*Pq/(qval*qval);    //this is now dimensionless...

  inten /= del;     //normalize by the thickness (in A)

  inten *= 1.0e8;   // 1/A to 1/cm

  return(inten+bkg);
}

LamellarModel :: LamellarModel() {
        scale      = Parameter(1.0);
        bi_thick     = Parameter(50.0, true);
        bi_thick.set_min(0.0);
        sld_bi    = Parameter(1.0e-6);
        sld_sol    = Parameter(6.3e-6);
        background = Parameter(0.0);
}

/**
 * Function to evaluate 1D scattering function
 * The NIST IGOR library is used for the actual calculation.
 * @param q: q-value
 * @return: function value
 */
double LamellarModel :: operator()(double q) {
        double dp[5];

        // Fill parameter array for IGOR library
        // Add the background after averaging
        dp[0] = scale();
        dp[1] = bi_thick();
        dp[2] = sld_bi();
        dp[3] = sld_sol();
        dp[4] = 0.0;

        // Get the dispersion points for the bi_thick
        vector<WeightPoint> weights_bi_thick;
        bi_thick.get_weights(weights_bi_thick);
        // Perform the computation, with all weight points
        double sum = 0.0;
        double norm = 0.0;

        // Loop over short_edgeA weight points
        for(int i=0; i< (int)weights_bi_thick.size(); i++) {
                dp[1] = weights_bi_thick[i].value;

                sum += weights_bi_thick[i].weight * lamellar_kernel(dp, q);
                norm += weights_bi_thick[i].weight;

        }

        return sum/norm + background();
}

/**
 * Function to evaluate 2D scattering function
 * @param q_x: value of Q along x
 * @param q_y: value of Q along y
 * @return: function value
 */

double LamellarModel :: operator()(double qx, double qy) {
        double q = sqrt(qx*qx + qy*qy);
        return (*this).operator()(q);
}

/**
 * Function to evaluate 2D scattering function
 * @param pars: parameters of the lamellar
 * @param q: q-value
 * @param phi: angle phi
 * @return: function value
 */
double LamellarModel :: evaluate_rphi(double q, double phi) {
        return (*this).operator()(q);
}
/**
 * Function to calculate effective radius
 * @return: effective radius value
 */
double LamellarModel :: calculate_ER() {
//NOT implemented yet!!!
        return 0.0;
}