Modified descriptor in magnetic field classes.

imagine/magnetic_fields/__init__.py

@@ -3,4 +3,6 @@
 from magnetic_field_factory import MagneticFieldFactory
 
 from magnetic_field import MagneticField
+
+from constant_field_factory import ConstantFieldFactory
 from jf12_factory import JF12Factory

imagine/magnetic_fields/jf12_factory.py

@@ -6,7 +6,9 @@ from magnetic_field_factory import MagneticFieldFactory
 class JF12Factory(MagneticFieldFactory):
     @property
     def descriptor(self):
-        return 'JF12'
+        result_descriptor = super(JF12Factory, self).descriptor
+        result_descriptor += ['JF12']
+        return result_descriptor
 
     def _initialize_parameter_defaults(self):
         self._parameter_defaults = {'b51_ran_b1': 10.8,

imagine/magnetic_fields/magnetic_field.py

@@ -11,9 +11,11 @@ class MagneticField(Loggable, object):
     def __init__(self, box_dimensions, resolution, descriptor,
                  parameters={}, create_array=None):
 
-        self._box_dimensions = box_dimensions
-        self._resolution = resolution
-        self._descriptor = str(descriptor)
+        self._box_dimensions = np.empty(3)
+        self._box_dimensions[:] = box_dimensions
+        self._resolution = np.empty(3)
+        self._resolution[:] = resolution
+        self._descriptor = descriptor
 
         self._parameters = {}
         for (key, value) in parameters.items():

imagine/magnetic_fields/magnetic_field_factory.py

@@ -20,7 +20,7 @@ class MagneticFieldFactory(Loggable, object):
 
     @abc.abstractproperty
     def descriptor(self):
-        raise NotImplementedError
+        return []
 
     def _initialize_parameter_defaults(self):
         self._parameter_defaults = {}