Alternative implementation of projection

[linpy.git] / pypol / domains.py

diff --git a/pypol/domains.py b/pypol/domains.py
index be87ffb..c844e55 100644 (file)
--- 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)