Changes in / [98c045a:89dba62] in sasmodels

Location:

sasmodels

Files:

• conversion_table.py (modified) (1 diff)
• convert.py (modified) (1 diff)
• kernel_iq.c (modified) (3 diffs)
• models/spherical_sld.py (modified) (7 diffs)
• models/unified_power_Rg.py (added)
• models/unified_power_rg.py (deleted)

sasmodels/conversion_table.py

@@ -854 +854 @@
             "TwoPowerLawModel",
         ],
-        "unified_power_rg": [
+        "unified_power_Rg": [
             "UnifiedPowerRg",
             dict(((field_new+str(index), field_old+str(index))

sasmodels/convert.py

@@ -606 +606 @@
             if pars['volfraction_a'] > 0.5:
                 pars['volfraction_a'] = 1.0 - pars['volfraction_a']
-        elif name == 'unified_power_rg':
+        elif name == 'unified_power_Rg':
             pars['level'] = int(pars['level'])
 

sasmodels/kernel_iq.c

@@ -85 +85 @@
 static void set_spin_weights(double in_spin, double out_spin, double weight[6])
 {
+
+  double norm;
   in_spin = clip(in_spin, 0.0, 1.0);
   out_spin = clip(out_spin, 0.0, 1.0);
@@ -94 +96 @@
   // However, since the weights are applied to the final intensity and
   // are not interned inside the I(q) function, we want the full
-  // weight and not the square root.  Any function using
-  // set_spin_weights as part of calculating an amplitude will need to
-  // manually take that square root, but there is currently no such
-  // function.
-  weight[0] = (1.0-in_spin) * (1.0-out_spin); // dd
-  weight[1] = (1.0-in_spin) * out_spin;       // du
-  weight[2] = in_spin * (1.0-out_spin);       // ud
-  weight[3] = in_spin * out_spin;             // uu
+  // weight and not the square root.  Anyway no function will ever use
+  // set_spin_weights as part of calculating an amplitude, as the weights are
+  // related to polarisation efficiency of the instrument. The weights serve to
+  // construct various magnet scattering cross sections, which are linear combinations
+  // of the spin-resolved cross sections. The polarisation efficiency e_in and e_out
+  // are parameters ranging from 0.5 (unpolarised) beam to 1 (perfect optics).
+  // For in_spin or out_spin <0.5 one assumes a CS, where the spin is reversed/flipped
+  // with respect to the initial supermirror polariser. The actual polarisation efficiency
+  // in this case is however e_in/out = 1-in/out_spin.
+
+  if (out_spin < 0.5){norm=1-out_spin;}
+  else{norm=out_spin;}
+
+
+// The norm is needed to make sure that the scattering cross sections are
+//correctly weighted, such that the sum of spin-resolved measurements adds up to
+// the unpolarised or half-polarised scattering cross section. No intensity weighting
+// needed on the incoming polariser side (assuming that a user), has normalised
+// to the incoming flux with polariser in for SANSPOl and unpolarised beam, respectively.
+
+
+  weight[0] = (1.0-in_spin) * (1.0-out_spin) / norm; // dd
+  weight[1] = (1.0-in_spin) * out_spin / norm;       // du
+  weight[2] = in_spin * (1.0-out_spin) / norm;       // ud
+  weight[3] = in_spin * out_spin / norm;             // uu
   weight[4] = weight[1]; // du.imag
   weight[5] = weight[2]; // ud.imag
@@ -119 +138 @@
     switch (xs) {
       default: // keep compiler happy; condition ensures xs in [0,1,2,3]
-      case 0: // uu => sld - D M_perpx
+      case 0: // dd => sld - D M_perpx
           return sld - px*perp;
-      case 1: // ud.real => -D M_perpy
+      case 1: // du.real => -D M_perpy
           return py*perp;
-      case 2: // du.real => -D M_perpy
+      case 2: // ud.real => -D M_perpy
           return py*perp;
-      case 3: // dd => sld + D M_perpx
+      case 3: // uu => sld + D M_perpx
           return sld + px*perp;
     }

sasmodels/models/spherical_sld.py

@@ -18 +18 @@
 sub-shell is described by a line function, with *n_steps* sub-shells per
 interface. The form factor is normalized by the total volume of the sphere.
+
+.. note::
+
+   *n_shells* must be an integer. *n_steps* must be an ODD integer.
 
 Interface shapes are as follows:
@@ -73 +77 @@
     3 \rho_\text{solvent} V(r_N)
     \Big[ \frac{\sin(qr_N) - qr_N \cos(qr_N)} {qr_N^3} \Big]
-
 
 Here we assumed that the SLDs of the core and solvent are constant in $r$.
@@ -156 +159 @@
     \end{align*}
 
-
 We assume $\rho_{\text{inter}_j} (r)$ is approximately linear
 within the sub-shell $j$.
@@ -179 +181 @@
     when $P(Q) * S(Q)$ is applied.
 
-
 References
 ----------
@@ -194 +195 @@
 
 Authorship and Verification
-----------------------------
+---------------------------
 
 * **Author:** Jae-Hie Cho **Date:** Nov 1, 2010
 * **Last Modified by:** Paul Kienzle **Date:** Dec 20, 2016
-* **Last Reviewed by:** Paul Butler **Date:** September 8, 2018
+* **Last Reviewed by:** Steve King **Date:** March 29, 2019
 * **Source added by :** Steve King **Date:** March 25, 2019
 """
@@ -207 +208 @@
 
 name = "spherical_sld"
-title = "Sperical SLD intensity calculation"
+title = "Spherical SLD intensity calculation"
 description = """
             I(q) =
@@ -219 +220 @@
 # pylint: disable=bad-whitespace, line-too-long
 #            ["name", "units", default, [lower, upper], "type", "description"],
-parameters = [["n_shells",             "",           1,      [1, 10],        "volume", "number of shells"],
+parameters = [["n_shells",             "",           1,      [1, 10],        "volume", "number of shells (must be integer)"],
               ["sld_solvent",          "1e-6/Ang^2", 1.0,    [-inf, inf],    "sld", "solvent sld"],
               ["sld[n_shells]",        "1e-6/Ang^2", 4.06,   [-inf, inf],    "sld", "sld of the shell"],