Fixed set_mean for von Mises Fisher

Author: FlorianPfaff

pyrecest/distributions/hypersphere_subset/von_mises_fisher_distribution.py

@@ -131,7 +131,7 @@ def mode(self):
         return self.mu
 
     def set_mean(self, new_mean):
-        self.set_mode(new_mean)
+        return self.set_mode(new_mean)
 
     def set_mode(self, new_mode):
         assert new_mode.shape == self.mu.shape