Magnetic fields should accept multiple wires (#35)

* fix

* test

* control data

* changelog

docs/source/changelog.rst

@@ -2,6 +2,13 @@
 Changelog
 =========
 
+**v0.4.1**
+==========
+Bugfix
+------
+- `#34 <https://github.com/Matheart/manim-physics/pull/35>`_ : Magnetic fields
+  now accept multiple wires
+
 **v0.4.0**
 ==========
 Breaking Changes

manim_physics/electromagnetism/magnetostatics.py

@@ -101,11 +101,12 @@ def _field_func(
         currents: Iterable[float],
     ):
         B_field = np.zeros(3)
-        for (r0, r1), I in it.product(*dls, currents):
-            dl = r1 - r0
-            r = p - r0
-            dist = np.linalg.norm(r)
-            if dist < 0.1:
-                return np.zeros(3)
-            B_field += np.cross(dl, r) * I / dist**4
+        for dl in dls:
+            for (r0, r1), I in it.product(dl, currents):
+                dr = r1 - r0
+                r = p - r0
+                dist = np.linalg.norm(r)
+                if dist < 0.1:
+                    return np.zeros(3)
+                B_field += np.cross(dr, r) * I / dist**4
         return B_field

tests/test_electromagnetism.py

@@ -22,3 +22,12 @@ def test_magnetic_field(scene):
     wire = Wire(Circle(2).rotate(PI / 2, UP))
     field = MagneticField(wire)
     scene.add(field, wire)
+
+
+@frames_comparison(base_scene=ThreeDScene)
+def test_magnetic_field_multiple_wires(scene):
+    wire1 = Wire(Circle(2).rotate(PI / 2, RIGHT).shift(UP * 2))
+    wire2 = Wire(Circle(2).rotate(PI / 2, RIGHT).shift(UP * -2))
+    mag_field = MagneticField(wire1, wire2)
+    scene.set_camera_orientation(PI / 3, PI / 4)
+    scene.add(wire1, wire2, mag_field)