New method Expression.subs

[linpy.git] / pypol / domains.py

diff --git a/pypol/domains.py b/pypol/domains.py
index 4a1f9aa..6060dc9 100644 (file)
--- a/pypol/domains.py
+++ b/pypol/domains.py
@@ -5,7 +5,7 @@ import re
 from . import islhelper
 
 from .islhelper import mainctx, libisl, isl_set_basic_sets
-from .linexprs import Expression
+from .linexprs import Expression, Symbol, symbolnames
 
 
 __all__ = [
@@ -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)
@@ -152,18 +152,18 @@ 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
+        symbols = symbolnames(symbols)
         islset = self._toislset(self.polyhedra, self.symbols)
-        for dim in dims:
-            if dim in symbols:
-                num = symbols.index(dim)
-                islbset = libisl.isl_set_drop_constraints_involving_dims(islset, libisl.isl_dim_set, num, 1)
-        return Polyhedron._fromislset(islbset, self.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)
@@ -241,6 +241,7 @@ class Domain:
             self._dimension = len(self._symbols)
             return self
 
+    @classmethod
     def _toislset(cls, polyhedra, symbols):
         polyhedron = polyhedra[0]
         islbset = polyhedron._toislbasicset(polyhedron.equalities,
@@ -337,6 +338,7 @@ class Domain:
     def tosympy(self):
         raise NotImplementedError
 
+
 def And(*domains):
     if len(domains) == 0:
         from .polyhedra import Universe