March-dollase parameter update

hexrd/powder/wppf/WPPF.py

@@ -1869,21 +1869,21 @@ def _set_phase_params_vals_to_class(
                 if atominfo_vary:
                     updated_atominfo = True
 
+            texture_model = self.texture_model.get(p)
+            pname = f"{p}_p_md"
+            if pname in params and hasattr(texture_model, 'P_MD'):
+                val = params[pname].value
+                # computespectrum() reads P_MD from self.params
+                self.params[pname].value = val
+                if texture_model.P_MD != val:
+                    texture_model.P_MD = val
+
         if updated_lp:
             self.calctth()
 
         if updated_lp or updated_atominfo:
             self.calcsf()
 
-        """
-        In case March-Dollase texture parameters were used, we can
-        update those here
-        """
-        name = f"{pre}p_md"
-        if name in params:
-            val = params[name].value
-            self.texture_model[p].P_MD = val
-
         self.phases.phase_fraction = pf / np.sum(pf)
 
     def on_smoothing_modified(self):

hexrd/powder/wppf/texture.py

@@ -740,7 +740,7 @@ def get_parameters(
 
         pname = f'{self.material.name}_p_md'
 
-        params.add(pname, value=1.0, vary=False)
+        params.add(pname, value=self.P_MD, min=1e-3, vary=vary)
 
         return params
 

tests/powder/wppf/test_wppf_texture.py

@@ -287,8 +287,9 @@ def test_wppf_march_dollase_texture(texture_instrument, texture_img_dict):
 
     R.Refine()
 
-    # P_MD refinement should not make Rwp worse
-    assert R.Rwp <= rwp_before_pmd + 1e-4
+    # P_MD should refine away from random and improve the fit
+    assert not np.isclose(R.params['Ni_p_md'].value, 1.0)
+    assert R.Rwp < rwp_before_pmd - 0.01
 
     # Test texture_index (polymorphic interface)
     ti = R.texture_index
@@ -359,7 +360,7 @@ def test_march_dollase_texture_factors(texture_instrument, texture_img_dict):
         'eta_step': 5,
     }
     R = Rietveld(**kwargs)
-    R.params['Ni_p_md'].value = 1.5
+    assert R.params['Ni_p_md'].value == 1.5  # taken from P_MD
 
     # calc_pf_rings should produce constant rings matching texture_factors
     md.calc_pf_rings(R.params)