Enhanced meet() and join() to accept a list of elements as argument.

src/sage/combinat/posets/lattices.py

@@ -109,7 +109,7 @@ def _repr_(self):
         return "Finite meet-semilattice containing %s elements"\
                 %self._hasse_diagram.order()
 
-    def meet(self,x,y):
+    def meet(self, x, y=None):
         r"""
         Return the meet of two elements in the lattice.
 
@@ -125,14 +125,14 @@ def meet(self,x,y):
             sage: D.meet(1, 4)
             1
 
-        If this method is used directly, it is not necessary to coerce
-        elements into the poset. (Trac #11292)  ::
+        Using list of elements as an argument. Meet of empty list is
+        the bottom element::
 
-            sage: D = Posets.DiamondPoset(5)
-            sage: D.meet(1, 0)
+            sage: B4=Posets.BooleanLattice(4)
+            sage: B4.meet([3,5,6])
             0
-            sage: D.meet(1, 4)
-            1
+            sage: B4.meet([])
+            15
 
         Test that this method also works for facade lattices::
 
@@ -143,8 +143,14 @@ def meet(self,x,y):
             0
 
         """
-        i, j = map(self._element_to_vertex,(x,y))
-        return self._vertex_to_element(self._hasse_diagram._meet[i,j])
+        if y is not None: # Handle basic case fast
+            i, j = map(self._element_to_vertex, (x,y))
+            return self._vertex_to_element(self._hasse_diagram._meet[i,j])
+        L = map(self._element_to_vertex, x)
+        m = self.cardinality()-1 # m = top element
+        for i in L:
+            m = self._hasse_diagram._meet[i, m]
+        return self._vertex_to_element(m)
 
 ####################################################################################
 
@@ -232,9 +238,15 @@ def _repr_(self):
         return "Finite join-semilattice containing %s elements"\
                 %self._hasse_diagram.order()
 
-    def join(self,x,y):
+    def join(self, x, y=None):
         r"""
-        Return the join of two elements in the lattice.
+        Return the join of given elements in the lattice.
+
+        INPUT:
+
+        -  ``x, y`` - two elements of the (semi)lattice OR
+
+        -  ``x`` - a list or tuple of elements
 
         EXAMPLES::
 
@@ -248,14 +260,14 @@ def join(self,x,y):
             sage: D.join(1, 0)
             1
 
-        If this method is used directly, it is not necessary to coerce
-        elements into the poset. (Trac #11292)  ::
+        Using list of elements as an argument. Join of empty list is
+        the bottom element::
 
-            sage: D = Posets.DiamondPoset(5)
-            sage: D.join(1, 0)
-            1
-            sage: D.join(1, 4)
-            4
+            sage: B4=Posets.BooleanLattice(4)
+            sage: B4.join([2,4,8])
+            14
+            sage: B4.join([])
+            0
 
         Test that this method also works for facade lattices::
 
@@ -266,8 +278,15 @@ def join(self,x,y):
             3
 
         """
-        i, j = map(self._element_to_vertex,(x,y))
-        return self._vertex_to_element(self._hasse_diagram._join[i,j])
+        if y is not None: # Handle basic case fast
+            i, j = map(self._element_to_vertex, (x,y))
+            return self._vertex_to_element(self._hasse_diagram._join[i,j])
+        L = map(self._element_to_vertex, x)
+        j = 0 # j = bottom element
+        for i in L:
+            j = self._hasse_diagram._join[i, j]
+        return self._vertex_to_element(j)
+
 
 ####################################################################################