Better document m-sources; closes #312 (#326)

emg3d/electrodes.py

@@ -472,7 +472,12 @@ def __init__(self, coordinates, strength=1.0):
 
 @utils._known_class
 class TxMagneticPoint(Source, Point):
-    """Magnetic point source.
+    r"""Magnetic point source.
+
+    Represented by an infinitesimal small magnetic dipole with a magnetic
+    moment of :math:`I^m ds` (as compared to a magnetic source generated by an
+    electric loop, which has a magnetic moment of :math:`I^m = i\omega\mu A
+    I^e`, where A is the area of the loop).
 
     .. note::
 
@@ -529,11 +534,12 @@ def __init__(self, coordinates, strength=1.0, length=1.0):
 
 @utils._known_class
 class TxMagneticDipole(Source, Dipole):
-    """Magnetic dipole source using a square loop perpendicular to the dipole.
+    r"""Magnetic dipole source using a square loop perpendicular to the dipole.
 
     The magnetic dipole source simulates a magnetic dipole with an electric
-    square loop perpendicular and at the center of the dipole. The area of the
-    loop corresponds to the dipole length, to represent the same strength.
+    square loop perpendicular and at the center of the dipole; :math:`I^m =
+    i\omega\mu A I^e`. The area A of the loop corresponds to the dipole length,
+    to represent the same strength.
 
 
     Parameters
@@ -654,7 +660,7 @@ def coordinates_abs(self, source):
 
 @utils._known_class
 class RxElectricPoint(Receiver, Point):
-    """Electric point receiver (point sampling the field).
+    """Electric point receiver [V/m] (point sampling the field).
 
 
     Parameters
@@ -686,7 +692,7 @@ def __init__(self, coordinates, relative=False, data_type='complex'):
 
 @utils._known_class
 class RxMagneticPoint(Receiver, Point):
-    """Magnetic point receiver (point sampling the field).
+    """Magnetic point receiver [A/m] (point sampling the field).
 
 
     Parameters