API: make optional arg nvars in method count

This change is on the methods `dd.cudd.BDD.count`
and `dd.cudd_zdd.ZDD.count`. The tests of method
`count` and the CHANGELOG are updated.

CHANGES.md

@@ -16,6 +16,9 @@ API:
   to `list` of `dd.cudd.Function`
 - multiple roots supported in `dd.cudd.BDD.dump` for
   file types other than DDDMP
+- method `count` of the classes
+  `dd.cudd.BDD` and `dd.cudd_zdd.ZDD`:
+  - make optional the argument `nvars`
 - `dd.autoref.BDD.load`:
   require file extension `.p` for pickle files
 

dd/cudd.pyx

@@ -854,14 +854,18 @@ cdef class BDD(object):
         r = cuddUniqueInter(self.manager, index, high.node, low.node)
         return wrap(self, r)
 
-    def count(self, Function u, int nvars):
+    def count(self, Function u, nvars=None):
         """Return number of models of node `u`.
 
         @param nvars: regard `u` as an operator that
             depends on `nvars` many variables.
+
+            If omitted, then assume those in `support(u)`.
         """
         assert u.manager == self.manager
         n = len(self.support(u))
+        if nvars is None:
+            nvars = n
         assert nvars >= n, (nvars, n)
         r = Cudd_CountMinterm(self.manager, u.node, nvars)
         assert r != CUDD_OUT_OF_MEM

dd/cudd_zdd.pyx

@@ -1030,17 +1030,21 @@ cdef class ZDD(object):
         assert w is not None
         return (v, w)
 
-    def count(self, Function u, int nvars):
+    def count(self, Function u, nvars=None):
         """Return nuber of models of node `u`.
 
         @param nvars: regard `u` as an operator that
             depends on `nvars` many variables.
+
+            If omitted, then assume those in `support(u)`.
         """
         logger.debug('count')
         assert u.manager == self.manager
         support = self.support(u)
         r = self._count(0, u, support, cache=dict())
         n_support = len(support)
+        if nvars == None:
+            nvars = n_support
         assert nvars >= n_support, (nvars, n_support)
         return r * 2**(nvars - n_support)
 

tests/common.py

@@ -254,7 +254,8 @@ def test_cofactor(self):
 
     def test_count(self):
         b = self.DD()
-        b.add_var('x')
+        # x
+        b.declare('x')
         u = b.add_expr('x')
         with assert_raises(AssertionError):
             b.count(u, 0)
@@ -264,7 +265,10 @@ def test_count(self):
         assert n == 2, n
         n = b.count(u, 3)
         assert n == 4, n
-        b.add_var('y')
+        n = b.count(u)
+        assert n == 1, n
+        # x /\ y
+        b.declare('y')
         u = b.add_expr('x /\ y')
         with assert_raises(AssertionError):
             b.count(u, 0)
@@ -276,6 +280,22 @@ def test_count(self):
         assert n == 2, n
         n = b.count(u, 5)
         assert n == 8, n
+        n = b.count(u)
+        assert n == 1, n
+        # x \/ ~ y
+        u = b.add_expr('x \/ ~ y')
+        with assert_raises(AssertionError):
+            b.count(u, 0)
+        with assert_raises(AssertionError):
+            b.count(u, 1)
+        n = b.count(u, 2)
+        assert n == 3, n
+        n = b.count(u, 3)
+        assert n == 6, n
+        n = b.count(u, 4)
+        assert n == 12, n
+        n = b.count(u)
+        assert n == 3, n
 
     def test_pick_iter(self):
         b = self.DD()