diff --git a/lib/Model.cpp b/lib/Model.cpp
index 37d1e5c..a517316 100644
--- a/lib/Model.cpp
+++ b/lib/Model.cpp
@@ -93,11 +93,27 @@ double DoubleModel::operator()(const double *data, const double *par) const
 }
 
 // model bind //////////////////////////////////////////////////////////////////
-DoubleFunction DoubleModel::getBind(const DVec &par) const
+DoubleFunction DoubleModel::fixArg(const DVec &arg) const
 {
-    auto modelWithVec = [this](const double *_arg, const DVec &_par)
-                              {return (*this)(_arg, _par.data());};
+    auto modelWithVec = [this](const DVec &x, const double *p)
+                        {return (*this)(x.data(), p);};
+    auto modelBind    = bind(modelWithVec, arg, _1);
+
+    return DoubleFunction(getNPar(), modelBind);
+}
+
+DoubleFunction DoubleModel::fixPar(const DVec &par) const
+{
+    auto modelWithVec = [this](const double *x, const DVec &p)
+                              {return (*this)(x, p.data());};
     auto modelBind    = bind(modelWithVec, _1, par);
 
     return DoubleFunction(getNArg(), modelBind);
 }
+
+DoubleFunction DoubleModel::toFunction(void) const
+{
+    auto func = [this](const double *x){return (*this)(x, x + getNArg());};
+
+    return DoubleFunction(getNArg() + getNPar(), func);
+}
diff --git a/lib/Model.hpp b/lib/Model.hpp
index 970c6e5..20c5a4a 100644
--- a/lib/Model.hpp
+++ b/lib/Model.hpp
@@ -52,8 +52,10 @@ public:
     double operator()(const std::vector<double> &data,
                       const std::vector<double> &par) const;
     virtual double operator()(const double *data, const double *par) const;
-    // model bind
-    DoubleFunction getBind(const DVec &par) const;
+    // bind
+    DoubleFunction fixArg(const DVec &arg) const;
+    DoubleFunction fixPar(const DVec &par) const;
+    DoubleFunction toFunction(void) const;
 private:
     // error checking
     void checkSize(const Index nArg, const Index nPar) const;
diff --git a/lib/XYStatData.cpp b/lib/XYStatData.cpp
index 2b2f6e3..c5f1910 100644
--- a/lib/XYStatData.cpp
+++ b/lib/XYStatData.cpp
@@ -247,7 +247,7 @@ FitResult XYStatData::fit(Minimizer &minimizer, const DVec &init,
     result.model_.resize(modelVector.size());
     for (unsigned int j = 0; j < modelVector.size(); ++j)
     {
-        result.model_[j] = modelVector[j]->getBind(result);
+        result.model_[j] = modelVector[j]->fixPar(result);
     }
     
     return result;