Fixing #81 in mapper (#105)

* if the first layer is trivial, it should not be ignored. Fixes #81

qiskit/_openquantumcompiler.py

@@ -37,7 +37,7 @@ def compile(qasm_circuit, basis_gates='u1,u2,u3,cx,id', coupling_map=None,
         initial_layout (dict): A mapping of qubit to qubit::
 
                               {
-                                ("q", strart(int)): ("q", final(int)),
+                                ("q", start(int)): ("q", final(int)),
                                 ...
                               }
                               eg.

qiskit/mapper/_mapping.py

@@ -332,8 +332,8 @@ def swap_mapper(circuit_graph, coupling_graph,
     # Schedule the input circuit
     layerlist = circuit_graph.layers()
     logger.debug("schedule:")
-    for i in range(len(layerlist)):
-        logger.debug("    %d: %s", i, layerlist[i]["partition"])
+    for i,v in enumerate(layerlist):
+        logger.debug("    %d: %s", (i, v["partition"]))
 
     if initial_layout is not None:
         # Check the input layout
@@ -372,13 +372,6 @@ def swap_mapper(circuit_graph, coupling_graph,
         logger.debug("swap_mapper: success_flag=%s,best_d=%s,trivial_flag=%s",
                      success_flag, str(best_d), trivial_flag)
 
-        # If this layer is only single-qubit gates,
-        # and we have yet to see multi-qubit gates,
-        # continue to the next iteration
-        if trivial_flag and first_layer:
-            logger.debug("swap_mapper: skip to next layer")
-            continue
-
         # If this fails, try one gate at a time in this layer
         if not success_flag:
             logger.debug("swap_mapper: failed, layer %d, "