Add in stub MDA dihedral casting convention. (#171)

* add in stub MDA cast

* fix

* increase amount of testing

distopia/tests/test_distopia.py

@@ -341,9 +341,9 @@ def test_dihedrals(self, dtype, positions):
         dihedrals = distopia.calc_dihedrals_no_box(a, b, c, d)
         # Check calculated values
         assert_equal(len(dihedrals), 4, err_msg="calc_dihedrals results have wrong length")
-        # FIXME: BROKEN assert np.isnan(dihedrals[0]), "Zero length dihedral failed"
-        # FIXME: BROKEN assert np.isnan(dihedrals[1]), "Straight line dihedral failed"
-        # FIXME: BROKEN assert_almost_equal(dihedrals[2], np.pi, self.prec, err_msg="180 degree dihedral failed")
+        assert np.isnan(dihedrals[0]), "Zero length dihedral failed"
+        assert np.isnan(dihedrals[1]), "Straight line dihedral failed"
+        assert_almost_equal(dihedrals[2], -np.pi, self.prec, err_msg="180 degree dihedral failed") # np.pi in MDAnalysis
         assert_almost_equal(dihedrals[3], -0.50714064, self.prec,
                             err_msg="arbitrary dihedral angle failed")
 

libdistopia/src/distopia.cpp

@@ -498,6 +498,11 @@ namespace distopia {
             // apply mask to set NAN where x and y are both zero
             auto fin = hn::IfThenElse(mask, hn::Set(d, NAN), res);
 
+
+            // check where it is exactly -np.pi and set to np.pi for compliance with mda code
+            // auto mask2 = hn::Eq(fin, hn::Set(d, -M_PI));
+            // fin = hn::IfThenElse(mask2, hn::Set(d, M_PI), fin);
+
             return fin;
         }
 

libdistopia/test/test_mda_match.cpp

@@ -14,7 +14,7 @@ typedef Types<float, double> ScalarTypes;
 
 // constants
 constexpr int BOXSIZE = 30;
-constexpr int NRESULTS = 10;
+constexpr int NRESULTS = 1000;
 constexpr int NINDICIES = 5;
 constexpr double abs_err = 1.0e-4;