source: sasview/sansmodels/src/sans/models/c_extensions/cylinder.c @ 19ef1e5

/**
 * Scattering model for a cylinder
 * @author: Mathieu Doucet / UTK
 */

#include "cylinder.h"
#include <math.h>
#include "libCylinder.h"
#include <stdio.h>
#include <stdlib.h>


/**
 * Function to evaluate 1D scattering function
 * @param pars: parameters of the cylinder
 * @param q: q-value
 * @return: function value
 */
double cylinder_analytical_1D(CylinderParameters *pars, double q) {
        double dp[5];
        
        // Fill paramater array
        dp[0] = pars->scale;
        dp[1] = pars->radius;
        dp[2] = pars->length;
        dp[3] = pars->contrast;
        dp[4] = pars->background;
        
        // Call library function to evaluate model
        return CylinderForm(dp, q);     
}

/**
 * Function to evaluate 2D scattering function
 * @param pars: parameters of the cylinder
 * @param q: q-value
 * @return: function value
 */
double cylinder_analytical_2DXY(CylinderParameters *pars, double qx, double qy) {
        double q;
        q = sqrt(qx*qx+qy*qy);
    return cylinder_analytical_2D_scaled(pars, q, qx/q, qy/q);
} 


/**
 * Function to evaluate 2D scattering function
 * @param pars: parameters of the cylinder
 * @param q: q-value
 * @param phi: angle phi
 * @return: function value
 */
double cylinder_analytical_2D(CylinderParameters *pars, double q, double phi) {
    return cylinder_analytical_2D_scaled(pars, q, cos(phi), sin(phi));
} 
        
/**
 * Function to evaluate 2D scattering function
 * @param pars: parameters of the cylinder
 * @param q: q-value
 * @param q_x: q_x / q
 * @param q_y: q_y / q
 * @return: function value
 */
double cylinder_analytical_2D_scaled(CylinderParameters *pars, double q, double q_x, double q_y) {
        double cyl_x, cyl_y, cyl_z;
        double q_z;
        double alpha, vol, cos_val;
        double answer;
        
    // Cylinder orientation
    cyl_x = sin(pars->cyl_theta) * cos(pars->cyl_phi);
    cyl_y = sin(pars->cyl_theta) * sin(pars->cyl_phi);
    cyl_z = cos(pars->cyl_theta);
     
    // q vector
    q_z = 0;
        
    // Compute the angle btw vector q and the
    // axis of the cylinder
    cos_val = cyl_x*q_x + cyl_y*q_y + cyl_z*q_z;
    
    // The following test should always pass
    if (fabs(cos_val)>1.0) {
        printf("cyl_ana_2D: Unexpected error: cos(alpha)>1\n");
        return 0;
    }
    
    // Note: cos(alpha) = 0 and 1 will get an
    // undefined value from CylKernel
        alpha = acos( cos_val );
        
        // Call the IGOR library function to get the kernel
        answer = CylKernel(q, pars->radius, pars->length/2.0, alpha) / sin(alpha);
        
        // Multiply by contrast^2
        answer *= pars->contrast*pars->contrast;
        
        //normalize by cylinder volume
        //NOTE that for this (Fournet) definition of the integral, one must MULTIPLY by Vcyl
    vol = acos(-1.0) * pars->radius * pars->radius * pars->length;
        answer *= vol;
        
        //convert to [cm-1]
        answer *= 1.0e8;
        
        //Scale
        answer *= pars->scale;
        
        // add in the background
        answer += pars->background;
        
        return answer;
}