diff --git a/latan/CompiledFunction.cpp b/latan/CompiledFunction.cpp
index 72c635c..c334c09 100644
--- a/latan/CompiledFunction.cpp
+++ b/latan/CompiledFunction.cpp
@@ -48,16 +48,10 @@ void CompiledDoubleFunction::setCode(const string &code)
 }
 
 // function call ///////////////////////////////////////////////////////////////
-double CompiledDoubleFunction::evaluate(const vector<double> &arg) const
+double CompiledDoubleFunction::operator()(const double *arg) const
 {
     double result;
     
-    if (arg.size() != getNArg())
-    {
-        LATAN_ERROR(Size, "function argument vector has a wrong size (got " +
-                    strFrom(arg.size()) + ", expected " + strFrom(getNArg()) +
-                    ")");
-    }
     for (unsigned int i = 0; i < getNArg(); ++i)
     {
         context_->vTable["x_" + strFrom(i)] = arg[i];
diff --git a/latan/CompiledFunction.hpp b/latan/CompiledFunction.hpp
index afb8f6e..75d1fde 100644
--- a/latan/CompiledFunction.hpp
+++ b/latan/CompiledFunction.hpp
@@ -45,10 +45,13 @@ public:
     // access
     void setCode(const std::string &code);
     // function call
-    virtual double evaluate(const std::vector<double> &arg) const;
+    using DoubleFunction::operator();
     // IO
     friend std::ostream & operator<<(std::ostream &out,
                                      CompiledDoubleFunction &f);
+private:
+    // function call
+    virtual double operator()(const double *arg) const;
 private:
     std::shared_ptr<MathInterpreter> interpreter_;
     std::shared_ptr<RunContext>      context_;
diff --git a/latan/Function.cpp b/latan/Function.cpp
index 4b701e5..737311e 100644
--- a/latan/Function.cpp
+++ b/latan/Function.cpp
@@ -61,25 +61,55 @@ unsigned int Function::getNArg(void) const
 // constructor /////////////////////////////////////////////////////////////////
 DoubleFunction::DoubleFunction(const unsigned nArg, vecFunc f)
 : Function(nArg)
-, buffer_(new vector<double>(nArg))
+, buffer_(new DVec(nArg))
 , f_(f)
 {}
 
 // function call ///////////////////////////////////////////////////////////////
-double DoubleFunction::evaluate(const std::vector<double> &arg) const
+double DoubleFunction::operator()(const double *arg) const
 {
     return f_(arg);
 }
 
+double DoubleFunction::operator()(const DVec &arg) const
+{
+    if (arg.size() != getNArg())
+    {
+        LATAN_ERROR(Size, "function argument vector has a wrong size (expected "
+                    + strFrom(getNArg()) + ", got " + strFrom(arg.size())
+                    + ")");
+    }
+    
+    return (*this)(arg.data());
+}
+
+double DoubleFunction::operator()(const std::vector<double> &arg) const
+{
+    if (arg.size() != getNArg())
+    {
+        LATAN_ERROR(Size, "function argument vector has a wrong size (expected "
+                    + strFrom(getNArg()) + ", got " + strFrom(arg.size())
+                    + ")");
+    }
+    
+    return (*this)(arg.data());
+}
+
 double DoubleFunction::operator()(std::stack<double> &arg) const
 {
     for (unsigned int i = 0; i < getNArg(); ++i)
     {
-        (*buffer_)[getNArg() - i - 1] = arg.top();
+        if (arg.empty())
+        {
+            LATAN_ERROR(Size, "function argument stack has a wrong size (expected "
+                        + strFrom(getNArg()) + ", got " + strFrom(i)
+                        + ")");
+        }
+        (*buffer_)(getNArg() - i - 1) = arg.top();
         arg.pop();
     }
     
-    return this->evaluate(*buffer_);
+    return (*this)(*buffer_);
 }
 
 double DoubleFunction::operator()(const double x0, ...) const
@@ -92,10 +122,10 @@ double DoubleFunction::operator()(const double x0, ...) const
         va_start(va, x0);
         for (unsigned int i = 1; i < getNArg(); ++i)
         {
-            (*buffer_)[i] = va_arg(va, double);
+            (*buffer_)(i) = va_arg(va, double);
         }
         va_end(va);
     }
     
-    return this->evaluate(*buffer_);
+    return (*this)(*buffer_);
 }
diff --git a/latan/Function.hpp b/latan/Function.hpp
index 5d07449..043801b 100644
--- a/latan/Function.hpp
+++ b/latan/Function.hpp
@@ -25,7 +25,6 @@
 #include <memory>
 #include <stack>
 #include <vector>
-#include <cstdarg>
 
 BEGIN_NAMESPACE
 
@@ -51,19 +50,23 @@ private:
 class DoubleFunction: public Function
 {
 private:
-    typedef std::function<double(const std::vector<double> &)> vecFunc;
+    typedef std::function<double(const double *)> vecFunc;
 public:
     // constructor
     explicit DoubleFunction(const unsigned nArg, vecFunc f = nullptr);
     // destructor
     virtual ~DoubleFunction(void) = default;
     // function call
-    virtual double evaluate(const std::vector<double> &arg) const;
+    double operator()(const DVec &arg) const;
+    double operator()(const std::vector<double> &arg) const;
     double operator()(std::stack<double> &arg) const;
     double operator()(const double x0, ...) const;
+protected:
+    // function call
+    virtual double operator()(const double *arg) const;
 private:
-    std::shared_ptr<std::vector<double>> buffer_;
-    vecFunc                              f_;
+    std::shared_ptr<DVec> buffer_;
+    vecFunc               f_;
 };
 
 END_NAMESPACE
diff --git a/latan/Math.cpp b/latan/Math.cpp
index 05e0831..3c65493 100644
--- a/latan/Math.cpp
+++ b/latan/Math.cpp
@@ -28,14 +28,14 @@ using namespace Latan;
  ******************************************************************************/
 
 #define DEF_STD_FUNC_1ARG(name) \
-static double name##VecFunc(const vector<double> &arg)\
+static double name##VecFunc(const double *arg)\
 {\
     return (name)(arg[0]);\
 }\
 DoubleFunction STDMATH_NAMESPACE::name(1, &name##VecFunc);
 
 #define DEF_STD_FUNC_2ARG(name) \
-static double name##VecFunc(const vector<double> &arg)\
+static double name##VecFunc(const double *arg)\
 {\
     return (name)(arg[0], arg[1]);\
 }\
diff --git a/latan/MinuitMinimizer.cpp b/latan/MinuitMinimizer.cpp
index 7f9e09c..92d5634 100644
--- a/latan/MinuitMinimizer.cpp
+++ b/latan/MinuitMinimizer.cpp
@@ -47,7 +47,7 @@ MinuitMinimizer::MinuitFunction::MinuitFunction(const DoubleFunction &f)
 double MinuitMinimizer::MinuitFunction::operator()
     (const vector<double> &x) const
 {
-    return f_->evaluate(x);
+    return (*f_)(x);
 }
 
 double MinuitMinimizer::MinuitFunction::Up(void) const