Fixed a bug in the apply_gate_to() function. Also clarified the spec.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402708

dlib/quantum_computing/quantum_computing.h

@@ -314,9 +314,9 @@ namespace dlib
                 {
                     if (temp.state_vector()(r) != qc_scalar_type(0))
                     {
-                        for (long c = 0; c < dims; ++c)
+                        for (long i = 0; i < dims; ++i)
                         {
-                            reg.state_vector()(c) += temp.state_vector()(r)*exp(r,c);
+                            reg.state_vector()(i) += temp.state_vector()(r)*exp(i,r);
                         }
                     }
                 }
@@ -458,7 +458,7 @@ namespace dlib
                 );
 
 
-            return rowm(data,row_idx)*reg;
+            return (data*reg)(row_idx);
         }
 
     private:

dlib/quantum_computing/quantum_computing_abstract.h

@@ -283,7 +283,8 @@ namespace dlib
                 
                 Then applying a composite gate to reg_all would give you the same thing as
                 applying the lhs gate to reg_high and the rhs gate to reg_low and then appending 
-                the two resulting registers.
+                the two resulting registers.  So the lhs gate of a composite_gate applies to
+                the high order bits of a regitser and the rhs gate applies to the lower order bits.
         !*/
     public: