diff --git a/lib/Function.cpp b/lib/Function.cpp
index 974a707..09c1873 100644
--- a/lib/Function.cpp
+++ b/lib/Function.cpp
@@ -105,12 +105,35 @@ double DoubleFunction::operator()(void) const
  ******************************************************************************/
 DSample DoubleFunctionSample::operator()(const DMatSample &arg) const
 {
-    DSample result(arg.size());
+    DSample result(size());
     
-    FOR_STAT_ARRAY(arg, s)
+    FOR_STAT_ARRAY((*this), s)
     {
         result[s] = (*this)[s](arg[s]);
     }
     
     return result;
 }
+
+DSample DoubleFunctionSample::operator()(const double *arg) const
+{
+    DSample result(size());
+    
+    FOR_STAT_ARRAY((*this), s)
+    {
+        result[s] = (*this)[s](arg);
+    }
+    
+    return result;
+}
+
+DSample DoubleFunctionSample::operator()(const DVec &arg) const
+{
+    return (*this)(arg.data());
+}
+
+DSample DoubleFunctionSample::operator()(const vector<double> &arg) const
+{
+    return (*this)(arg.data());
+}
+
diff --git a/lib/Function.hpp b/lib/Function.hpp
index b3555f0..dd37374 100644
--- a/lib/Function.hpp
+++ b/lib/Function.hpp
@@ -86,8 +86,21 @@ public:
     virtual ~DoubleFunctionSample(void) = default;
     // function call
     DSample operator()(const DMatSample &arg) const;
+    DSample operator()(const double *arg) const;
+    DSample operator()(const DVec &arg) const;
+    DSample operator()(const std::vector<double> &arg) const;
+    template <typename... Ts>
+    DSample operator()(const double arg0, const Ts... args) const;
 };
 
+template <typename... Ts>
+DSample DoubleFunctionSample::operator()(const double arg0,
+                                        const Ts... args) const
+{
+    const double arg[] = {arg0, args...};
+    
+    return (*this)(arg);
+}
 
 END_NAMESPACE