1 | #define INVALID(v) (v.radius_cap < v.radius) |
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2 | |
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3 | // Integral over a convex lens kernel for t in [h/R,1]. See the docs for |
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4 | // the definition of the function being integrated. |
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5 | // q is the magnitude of the q vector. |
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6 | // h is the length of the lens "inside" the cylinder. This negative wrt the |
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7 | // definition of h in the docs. |
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8 | // radius_cap is the radius of the lens |
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9 | // length is the cylinder length, or the separation between the lens halves |
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10 | // theta is the angle of the cylinder wrt q. |
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11 | static double |
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12 | _cap_kernel(double qab, double qc, double h, double radius_cap, |
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13 | double half_length) |
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14 | { |
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15 | // translate a point in [-1,1] to a point in [lower,upper] |
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16 | const double upper = 1.0; |
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17 | const double lower = h/radius_cap; // integral lower bound |
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18 | const double zm = 0.5*(upper-lower); |
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19 | const double zb = 0.5*(upper+lower); |
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20 | |
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21 | // cos term in integral is: |
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22 | // cos (q (R t - h + L/2) cos(theta)) |
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23 | // so turn it into: |
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24 | // cos (m t + b) |
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25 | // where: |
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26 | // m = q R cos(theta) |
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27 | // b = q(L/2-h) cos(theta) |
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28 | const double m = radius_cap*qc; // cos argument slope |
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29 | const double b = (half_length-h)*qc; // cos argument intercept |
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30 | const double qab_r = radius_cap*qab; // Q*R*sin(theta) |
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31 | double total = 0.0; |
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32 | for (int i=0; i<76 ;i++) { |
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33 | const double t = Gauss76Z[i]*zm + zb; |
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34 | const double radical = 1.0 - t*t; |
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35 | const double bj = sas_2J1x_x(qab_r*sqrt(radical)); |
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36 | const double Fq = cos(m*t + b) * radical * bj; |
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37 | total += Gauss76Wt[i] * Fq; |
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38 | } |
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39 | // translate dx in [-1,1] to dx in [lower,upper] |
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40 | const double integral = total*zm; |
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41 | const double cap_Fq = 2.0*M_PI*cube(radius_cap)*integral; |
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42 | return cap_Fq; |
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43 | } |
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44 | |
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45 | static double |
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46 | _fq(double qab, double qc, double h, double radius_cap, double radius, double half_length) |
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47 | { |
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48 | const double cap_Fq = _cap_kernel(qab, qc, h, radius_cap, half_length); |
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49 | const double bj = sas_2J1x_x(radius*qab); |
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50 | const double si = sas_sinx_x(half_length*qc); |
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51 | const double cyl_Fq = 2.0*M_PI*radius*radius*half_length*bj*si; |
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52 | const double Aq = cap_Fq + cyl_Fq; |
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53 | return Aq; |
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54 | } |
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55 | |
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56 | static double |
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57 | form_volume(double radius, double radius_cap, double length) |
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58 | { |
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59 | // cap radius should never be less than radius when this is called |
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60 | |
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61 | // Note: volume V = 2*V_cap + V_cyl |
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62 | // |
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63 | // V_cyl = pi r_cyl^2 L |
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64 | // V_cap = 1/6 pi h_c (3 r_cyl^2 + h_c^2) = 1/3 pi h_c^2 (3 r_cap - h_c) |
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65 | // |
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66 | // The docs for capped cylinder give the volume as: |
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67 | // V = pi r^2 L + 2/3 pi (R-h)^2 (2R + h) |
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68 | // where r_cap=R and h = R - h_c. |
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69 | // |
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70 | // The first part is clearly V_cyl. The second part requires some work: |
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71 | // (R-h)^2 => h_c^2 |
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72 | // (2R+h) => 2R+ h_c-h_c + h => 2R + (R-h)-h_c + h => 3R-h_c |
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73 | // And so: |
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74 | // 2/3 pi (R-h)^2 (2R + h) => 2/3 pi h_c^2 (3 r_cap - h_c) |
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75 | // which is 2 V_cap, using the second form above. |
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76 | // |
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77 | // In this function we are going to use the first form of V_cap |
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78 | // |
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79 | // V = V_cyl + 2 V_cap |
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80 | // = pi r^2 L + pi hc (r^2 + hc^2/3) |
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81 | // = pi (r^2 (L+hc) + hc^3/3) |
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82 | const double hc = radius_cap - sqrt(radius_cap*radius_cap - radius*radius); |
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83 | return M_PI*(radius*radius*(length+hc) + hc*hc*hc/3.0); |
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84 | } |
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85 | |
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86 | static double |
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87 | Iq(double q, double sld, double solvent_sld, |
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88 | double radius, double radius_cap, double length) |
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89 | { |
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90 | const double h = sqrt(radius_cap*radius_cap - radius*radius); |
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91 | const double half_length = 0.5*length; |
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92 | |
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93 | // translate a point in [-1,1] to a point in [0, pi/2] |
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94 | const double zm = M_PI_4; |
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95 | const double zb = M_PI_4; |
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96 | double total = 0.0; |
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97 | for (int i=0; i<76 ;i++) { |
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98 | const double theta = Gauss76Z[i]*zm + zb; |
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99 | double sin_theta, cos_theta; // slots to hold sincos function output |
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100 | SINCOS(theta, sin_theta, cos_theta); |
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101 | const double qab = q*sin_theta; |
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102 | const double qc = q*cos_theta; |
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103 | const double Aq = _fq(qab, qc, h, radius_cap, radius, half_length); |
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104 | // scale by sin_theta for spherical coord integration |
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105 | total += Gauss76Wt[i] * Aq * Aq * sin_theta; |
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106 | } |
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107 | // translate dx in [-1,1] to dx in [lower,upper] |
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108 | const double form = total * zm; |
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109 | |
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110 | // Contrast |
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111 | const double s = (sld - solvent_sld); |
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112 | return 1.0e-4 * s * s * form; |
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113 | } |
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114 | |
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115 | |
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116 | static double |
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117 | Iqxy(double qab, double qc, |
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118 | double sld, double solvent_sld, double radius, |
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119 | double radius_cap, double length) |
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120 | { |
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121 | const double h = sqrt(radius_cap*radius_cap - radius*radius); |
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122 | const double Aq = _fq(qab, qc, h, radius_cap, radius, 0.5*length); |
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123 | |
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124 | // Multiply by contrast^2 and convert to cm-1 |
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125 | const double s = (sld - solvent_sld); |
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126 | return 1.0e-4 * square(s * Aq); |
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127 | } |
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