fixed bugs, added .gigtignore

.gitignore

+*__pycache__
\ No newline at end of file

__main__.py

+import elements
+import graphics
+
+print("Hi World!")

elements/__init__.py

 import numpy as np
 import cmath
+
+from .main import *

elements/main.py

+import numpy as np
+
 ### ------ Special elements ------
 class Source:
     def __init__(self, initial_vector=np.array([1., 0.+0j])): ## if no input state given, starts a |0>
@@ -13,11 +15,12 @@ class Screen:
         self.previous = previous
 
     def show(self):
-        previous_component, previous_component_output_side = previous
+        previous_component, previous_component_output_side = self.previous
         print(previous_component.out(previous_component_output_side))
 
     def out(self):
-        return previous_component.out(previous_component_output_site)
+        previous_component, previous_component_output_side = self.previous
+        return previous_component.out(previous_component_output_side)
 
 
 
@@ -28,19 +31,21 @@ class Element:
         self.next = None
 
 class Plate(Element):
-    def __init__(self, jones_matrix = np.eye((2, 2), dtype='complex')):
+    def __init__(self, previous, jones_matrix = np.eye(2, dtype='complex')):
+        Element.__init__(self, previous)
         self.jones_matrix = jones_matrix
         self.output_vector = None
 
     def out(self, side):
         previous_element = self.previous[0]
         previous_element_output_side = self.previous[1]
-        self.output_vector = self.jones_matrix @ previous_element(previous_element_output_side) # matrix-vector product : jones matrix times state vector given by the out(side) method of the previous component
+        self.output_vector = self.jones_matrix @ previous_element.out(previous_element_output_side) # matrix-vector product : jones matrix times state vector given by the out(side) method of the previous component
         return self.output_vector
 
 class BeamSplitter(Element):
     """matrix is a 4x4 complex ndarray, two first dimensions regard left input, two next are right. So it's blockwise defined."""
-    def __init__(self, matrix = np.eye((4, 4), dtype='complex')):
+    def __init__(self, previous, matrix = np.eye(4, dtype='complex')):
+        Element.__init__(self, previous)
         self.matrix = matrix
         self.output_vector = None