minimal code for part 1.

RubberBand.py

@@ -0,0 +1,35 @@
+import numpy as np
+
+from Link import Link
+
+class RubberBand:
+    def __init__(self, N, a=1.):
+        """
+        RubberBand is a class that can simulate a rubber band with N
+        incompressible links of length a.
+
+        Parameters:
+            N (int)     The number of links.
+            a (float)   The fixed length of links.
+        """
+
+        self.N = N
+        self.a = a
+        self.links = self.__sample_links()
+
+    @property
+    def length(self):
+        return self.a * np.sum([l.direction for l in self.links])
+
+    def __sample_links(self):
+        """
+        Sample N Link objects with a random direction.
+        """
+
+        samples = np.random.random_sample((self.N,))
+        directions = np.ones(samples.shape)
+        directions[samples < 0.5] = -1.
+        directions = directions.astype(int)
+        return [Link(d) for d in directions]
+
+