add doc to bloch

dptb/negf/bloch.py

@@ -2,7 +2,9 @@
 import numpy as np
 
 
+# The Bloch class in Python defines a method to unfold k points based on a given Bloch factor.
 class Bloch(object):
+
     def __init__(self,bloch_factor) -> None:
 
         if  isinstance(bloch_factor,list):
@@ -12,9 +14,31 @@ def __init__(self,bloch_factor) -> None:
         self.bloch_factor = bloch_factor
 
 
-    def unfold_points(self,k):
+    def unfold_points(self,k:list) -> np.ndarray:
+        '''The `unfold_points` function generates expansion k points based on Bloch theorem and reshapes the
+        output into a specific format.
+        
+        Parameters
+        ----------
+        k
+            The `k` parameter in the `unfold_points` method represents the original k-point in the Brillouin zone.
+        
+        Returns
+        -------
+            The `unfold_points` method returns a reshaped array of expansion points calculated based on the
+        input parameter `k` and the bloch factor `B`. The expansion points are created using B-casting rules
+        and then reshaped into a 2D array with 3 columns.
+        
+        '''
 
-
+        # check k is a 3D vector
+        if isinstance(k,list):
+            assert len(k) == 3, "kpoint should be a 3D vector"
+        elif isinstance(k,np.ndarray):
+            assert k.shape[0] == 3, "kpoint should be a 3D vector"
+        else:
+            raise ValueError("k should be a list or numpy array")
+
         # Create expansion points
         B = self.bloch_factor
         unfold = np.empty([B[2], B[1], B[0], 3])