Ticket #12244: trac_12244.patch

sage/graphs/distances_all_pairs.pyx

@@ -276 +276 @@
 # Predecessors #
 ################
 
-cdef unsigned short * c_shortest_path_all_pairs(G):
+cdef unsigned short * c_shortest_path_all_pairs(G) except NULL:
     r"""
     Returns the matrix of predecessors in G.
 
@@ -327 +327 @@
     """
 
     cdef int n = G.order()
+    
+    if n == 0:
+        return {}
 
     cdef unsigned short * predecessors = c_shortest_path_all_pairs(G)
     cdef unsigned short * c_predecessors = predecessors
@@ -404 +407 @@
     from sage.rings.infinity import Infinity
 
     cdef int n = G.order()
+
+    if n == 0:
+        return {}
+
     cdef unsigned short * distances = c_distances_all_pairs(G)
     cdef unsigned short * c_distances = distances
 
@@ -481 +488 @@
 
     from sage.rings.infinity import Infinity
     cdef int n = G.order()
+    
+    if n == 0:
+        return {}, {}
+
     cdef unsigned short * distances = <unsigned short *> sage_malloc(n*n*sizeof(unsigned short *))
     cdef unsigned short * c_distances = distances
     cdef unsigned short * predecessor = <unsigned short *> sage_malloc(n*n*sizeof(unsigned short *))
@@ -527 +538 @@
 # Eccentricity #
 ################
 
-cdef unsigned short * c_eccentricity(G):
+cdef unsigned short * c_eccentricity(G) except NULL:
     r"""
     Returns the vector of eccentricities in G.
 
@@ -559 +570 @@
     """
     from sage.rings.infinity import Infinity
     cdef int n = G.order()
+
+    if n == 0:
+        return []
+
     cdef unsigned short * ecc = c_eccentricity(G)
 
     cdef list l_ecc = []
@@ -691 +706 @@
 
     cdef list gverts = g.verts()
 
+    if gverts == []:
+        if distances and paths:
+            return {}, {}
+        else:
+            return {}
+
     cdef int n = max(gverts) + 1
 
     if n >= <unsigned short> -1:

sage/graphs/generic_graph.py

@@ -10543 +10543 @@
             2
             sage: G.diameter()
             2
-        """
+
+        TEST::
+
+            sage: g = Graph()
+            sage: g.radius()
+            Traceback (most recent call last):
+            ...
+            ValueError: This method has no meaning on empty graphs.
+        """
+        if self.order() == 0:
+            raise ValueError("This method has no meaning on empty graphs.")
+
         return min(self.eccentricity())
     
     def center(self):
@@ -11467 +11478 @@
         the theory of the Wiener number. INDIAN JOURNAL OF CHEMISTRY SECTION A
         PUBLICATIONS & INFORMATION DIRECTORATE, CSIR
         """
-
         return sum([sum(v.itervalues()) for v in self.distance_all_pairs().itervalues()])/2
 
     def average_distance(self):
@@ -11493 +11503 @@
         .. [GYLL93] I. Gutman, Y.-N. Yeh, S.-L. Lee, and Y.-L. Luo. Some recent
           results in the theory of the Wiener number. *Indian Journal of
           Chemistry*, 32A:651--661, 1993.
-        """
+
+        TEST::
+
+            sage: g = Graph()
+            sage: g.average_distance()
+            Traceback (most recent call last):
+            ...
+            ValueError: The graph must have at least two vertices for this value to be defined
+        """
+        if self.order() < 2:
+            raise ValueError("The graph must have at least two vertices for this value to be defined")
 
         return Integer(self.wiener_index())/Integer((self.order()*(self.order()-1))/2)