Polyhedron() constructor can return Empty or Universe

[linpy.git] / linpy / polyhedra.py

diff --git a/linpy/polyhedra.py b/linpy/polyhedra.py
index c05432a..820b014 100644 (file)
--- a/linpy/polyhedra.py
+++ b/linpy/polyhedra.py
@@ -94,15 +94,23 @@ class Polyhedron(Domain):
         sc_equalities = []
         if equalities is not None:
             for equality in equalities:
-                if not isinstance(equality, LinExpr):
-                    raise TypeError('equalities must be linear expressions')
-                sc_equalities.append(equality.scaleint())
+                if isinstance(equality, LinExpr):
+                    sc_equalities.append(equality.scaleint())
+                elif isinstance(equality, numbers.Rational):
+                    sc_equalities.append(Rational(equality).scaleint())
+                else:
+                    raise TypeError('equalities must be linear expressions '
+                        'or rational numbers')
         sc_inequalities = []
         if inequalities is not None:
             for inequality in inequalities:
-                if not isinstance(inequality, LinExpr):
-                    raise TypeError('inequalities must be linear expressions')
-                sc_inequalities.append(inequality.scaleint())
+                if isinstance(inequality, LinExpr):
+                    sc_inequalities.append(inequality.scaleint())
+                elif isinstance(inequality, numbers.Rational):
+                    sc_inequalities.append(Rational(inequality).scaleint())
+                else:
+                    raise TypeError('inequalities must be linear expressions '
+                        'or rational numbers')
         symbols = cls._xsymbols(sc_equalities + sc_inequalities)
         islbset = cls._toislbasicset(sc_equalities, sc_inequalities, symbols)
         return cls._fromislbasicset(islbset, symbols)
@@ -214,6 +222,10 @@ class Polyhedron(Domain):
 
     @classmethod
     def _fromislbasicset(cls, islbset, symbols):
+        if bool(libisl.isl_basic_set_is_empty(islbset)):
+            return Empty
+        if bool(libisl.isl_basic_set_is_universe(islbset)):
+            return Universe
         islconstraints = islhelper.isl_basic_set_constraints(islbset)
         equalities = []
         inequalities = []
@@ -318,10 +330,10 @@ class Polyhedron(Domain):
             return 'And({})'.format(', '.join(strings))
 
     @classmethod
-    def fromsympy(cls, expr):
-        domain = Domain.fromsympy(expr)
+    def fromsympy(cls, expression):
+        domain = Domain.fromsympy(expression)
         if not isinstance(domain, Polyhedron):
-            raise ValueError('non-polyhedral expression: {!r}'.format(expr))
+            raise ValueError('non-polyhedral expression: {!r}'.format(expression))
         return domain
 
     def tosympy(self):
@@ -380,75 +392,75 @@ Universe = UniverseType()
 
 def _pseudoconstructor(func):
     @functools.wraps(func)
-    def wrapper(expr1, expr2, *exprs):
-        exprs = (expr1, expr2) + exprs
-        for expr in exprs:
-            if not isinstance(expr, LinExpr):
-                if isinstance(expr, numbers.Rational):
-                    expr = Rational(expr)
+    def wrapper(expression1, expression2, *expressions):
+        expressions = (expression1, expression2) + expressions
+        for expression in expressions:
+            if not isinstance(expression, LinExpr):
+                if isinstance(expression, numbers.Rational):
+                    expression = Rational(expression)
                 else:
                     raise TypeError('arguments must be rational numbers '
                         'or linear expressions')
-        return func(*exprs)
+        return func(*expressions)
     return wrapper
 
 @_pseudoconstructor
-def Lt(*exprs):
+def Lt(*expressions):
     """
     Create the polyhedron with constraints expr1 < expr2 < expr3 ...
     """
     inequalities = []
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         inequalities.append(right - left - 1)
     return Polyhedron([], inequalities)
 
 @_pseudoconstructor
-def Le(*exprs):
+def Le(*expressions):
     """
     Create the polyhedron with constraints expr1 <= expr2 <= expr3 ...
     """
     inequalities = []
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         inequalities.append(right - left)
     return Polyhedron([], inequalities)
 
 @_pseudoconstructor
-def Eq(*exprs):
+def Eq(*expressions):
     """
     Create the polyhedron with constraints expr1 == expr2 == expr3 ...
     """
     equalities = []
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         equalities.append(left - right)
     return Polyhedron(equalities, [])
 
 @_pseudoconstructor
-def Ne(*exprs):
+def Ne(*expressions):
     """
     Create the domain such that expr1 != expr2 != expr3 ... The result is a
     Domain object, not a Polyhedron.
     """
     domain = Universe
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         domain &= ~Eq(left, right)
     return domain
 
 @_pseudoconstructor
-def Ge(*exprs):
+def Ge(*expressions):
     """
     Create the polyhedron with constraints expr1 >= expr2 >= expr3 ...
     """
     inequalities = []
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         inequalities.append(left - right)
     return Polyhedron([], inequalities)
 
 @_pseudoconstructor
-def Gt(*exprs):
+def Gt(*expressions):
     """
     Create the polyhedron with constraints expr1 > expr2 > expr3 ...
     """
     inequalities = []
-    for left, right in zip(exprs, exprs[1:]):
+    for left, right in zip(expressions, expressions[1:]):
         inequalities.append(left - right - 1)
     return Polyhedron([], inequalities)