From 4ae512f39c14835badbfab6fc1ce877f601d104e Mon Sep 17 00:00:00 2001
From: Vivien Maisonneuve <v.maisonneuve@gmail.com>
Date: Tue, 1 Jul 2014 18:47:54 +0200
Subject: [PATCH 1/1] Alternative implementation of projection

---
 pypol/domains.py            | 26 +++++++++++---------------
 pypol/tests/test_domains.py | 10 +++++-----
 2 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/pypol/domains.py b/pypol/domains.py
index be87ffb..c844e55 100644
--- a/pypol/domains.py
+++ b/pypol/domains.py
@@ -139,7 +139,7 @@ class Domain:
 
     def simplify(self):
         #does not change anything in any of the examples
-        #isl seems to do this naturally 
+        #isl seems to do this naturally
         islset = self._toislset(self.polyhedra, self.symbols)
         islset = libisl.isl_set_remove_redundancies(islset)
         return self._fromislset(islset, self.symbols)
@@ -152,21 +152,17 @@ class Domain:
         islbset = libisl.isl_set_polyhedral_hull(islset)
         return Polyhedron._fromislbasicset(islbset, self.symbols)
 
-    def drop_dims(self, dims):
-        # use to remove certain variables use isl_set_drop_constraints_involving_dims instead?
-        from .polyhedra import Polyhedron      
-        dims = list(dims)
-        symbols = list(self.symbols)
+    def project_out(self, symbols):
+        # use to remove certain variables
         islset = self._toislset(self.polyhedra, self.symbols)
-        for dim in dims:
-            if dim in symbols:
-                first = symbols.index(dim)
-                islbset = libisl.isl_set_project_out(islset, libisl.isl_dim_set, first, 1)  
-                symbols.__delitem__(first)     
-            else:
-                islbset = libisl.isl_set_project_out(islset, libisl.isl_dim_set, 0, 0)        
-        return Polyhedron._fromislset(islbset, symbols)
-    
+        # the trick is to walk symbols in reverse order, to avoid index updates
+        for index, symbol in reversed(list(enumerate(self.symbols))):
+            if symbol in symbols:
+                islset = libisl.isl_set_project_out(islset, libisl.isl_dim_set, index, 1)
+        # remaining symbols
+        symbols = [symbol for symbol in self.symbols if symbol not in symbols]
+        return Domain._fromislset(islset, symbols)
+
     def sample(self):
         from .polyhedra import Polyhedron
         islset = self._toislset(self.polyhedra, self.symbols)
diff --git a/pypol/tests/test_domains.py b/pypol/tests/test_domains.py
index 692627c..55853fd 100644
--- a/pypol/tests/test_domains.py
+++ b/pypol/tests/test_domains.py
@@ -77,11 +77,11 @@ class TestDomain(unittest.TestCase):
     def test_polyhedral_hull(self):
         self.assertEqual(self.square1.polyhedral_hull(), self.hull)
 
-    def test_drop_dims(self):
-        self.assertEqual(self.square1.drop_dims('x'), self.dropped)
-        self.assertEqual(self.square1.drop_dims('x y'), self.universe)
-        self.assertEqual(self.universe.drop_dims(' '), self.universe)
-        self.assertEqual(self.empty.drop_dims(' '), Empty)
+    def test_project_out(self):
+        self.assertEqual(self.square1.project_out('x'), self.dropped)
+        self.assertEqual(self.square1.project_out('x y'), self.universe)
+        self.assertEqual(self.universe.project_out(' '), self.universe)
+        self.assertEqual(self.empty.project_out(' '), Empty)
 
     def test_simplify(self):
         self.assertEqual(self.universe.simplify(), self.universe)
-- 
2.20.1