Fix Ex slicing error.

Author: Kasper Peeters

core/pythoncdb/py_ex.cc

@@ -383,22 +383,21 @@ namespace cadabra {
 		Ex result;
 
 		pybind11::size_t start, stop, step, length;
-		slice.compute(ex->size(), &start, &stop, &step, &length);
+		// std::cerr << "SLICE object has " << ex->number_of_children(ex->begin()) << " elements" << std::endl;
+		slice.compute(ex->number_of_children(ex->begin()), &start, &stop, &step, &length);
+		// std::cerr << "SLICE: " << start << ", " << stop << ", " << step << ", " << length << std::endl;
 		if (length == 0)
 			return result;
 
 		// Set head
 		auto it = result.set_head(*ex->begin());
 
 		// Iterate over fully-closed range.
-		for (; start != stop; start += step) {
-			Ex::iterator toadd(ex->begin());
+		for (; start < stop; start += step) {
+			Ex::sibling_iterator toadd=ex->begin(ex->begin());
 			std::advance(toadd, start);
-			result.append_child(it, toadd);
+			result.append_child(it, Ex::iterator(toadd));
 			}
-		Ex::iterator toadd(ex->begin());
-		std::advance(toadd, start);
-		result.append_child(it, toadd);
 		return result;
 		}
 

tests/programming.cdb

@@ -370,3 +370,40 @@ def test17():
 
 test17()
 
+
+#  {i,j,k,l}::Indices(cartesian, values={x,y,z}).
+#  {\mu,\nu,\rho,\sigma}::Indices(polar, values={r,\theta,\phi}).
+#  ex:= x^{i} x^{i} + p_{\mu} p^{\mu};
+#  for node in ex:
+#       prop = Indices.get(node)
+#       if prop is not None:
+#           print(node)
+#           print(node.name, prop.values)
+#  
+#  ind = Indices.get($i$);
+
+def test18():
+    ex:= A + B + C + D + E;
+    s1 = ex[0:2]
+    tst:= A + B - @(s1);
+    assert(tst==0)
+    print("Test 18a passed")
+    s2 = ex[0:-2:2]
+    tst:= A + C - @(s2);
+    assert(tst==0)
+    print("Test 18b passed")
+    ex:= A + B + C + D + E + F;     
+    s3 = ex[0:-2:2]
+    tst:= A + C - @(s3);
+    print("Test 18c passed")
+    ex:= A + B + C + D + E + F;     
+    s4 = ex[1:-2:2]
+    tst:= B + D - @(s4);
+    print("Test 18d passed")
+    ex:= A + B + C + D + E;
+    s5 = ex[2:3]
+    tst:= C - @(s5);
+    assert(tst==0)
+    print("Test 18e passed")
+
+test18()