diff --git a/lib/optimization/loss_func.cpp b/lib/optimization/loss_func.cpp
index 26464cf..ce890a5 100644
--- a/lib/optimization/loss_func.cpp
+++ b/lib/optimization/loss_func.cpp
@@ -29,12 +29,13 @@
 
 gctl::loss_func::loss_func()
 {
-    uncer_type_ = 0;
+    init_ = false;
+    tnum_ = 0;
+    ntype_ = L2;
 }
 
 gctl::loss_func::loss_func(const array<double> &tar, norm_type_e n_type)
 {
-    uncer_type_ = 0;
     init(tar, n_type);
 }
 
@@ -42,59 +43,61 @@ gctl::loss_func::~loss_func(){}
 
 void gctl::loss_func::init(const array<double> &tar, norm_type_e n_type)
 {
-    tar_num_ = tar.size();
+    tnum_ = tar.size();
+    diff_.resize(tnum_);
+    us_.resize(tnum_, 1.0);
     tars_ = tar;
-    norm_type_ = n_type;
+    ntype_ = n_type;
+    init_ = true;
     return;
 }
 
 void gctl::loss_func::set_uncertainty(double uncer)
 {
-    uncer_type_ = 1;
-    uncer_ = uncer;
+    if (!init_) throw std::runtime_error("[gctl::loss_func] Not initialized.");
+    us_.resize(tnum_, uncer);
     return;
 }
 
 void gctl::loss_func::set_uncertainty(const array<double> &uncer)
 {
-    uncer_type_ = 2;
-    uncers_ = uncer;
+    if (!init_) throw std::runtime_error("[gctl::loss_func] Not initialized.");
+    if (uncer.size() != tnum_) throw std::runtime_error("[gctl::loss_func] Invalid array size.");
+    us_ = uncer;
     return;
 }
 
-double gctl::loss_func::get_loss()
+double gctl::loss_func::evaluate(const array<double> &x, array<double> &g)
 {
-    double l = loss_;
-    loss_ = 0.0;
-    return l;
+    if (!init_) throw std::runtime_error("[gctl::loss_func] Not initialized.");
+    if (x.size() != tnum_) throw std::runtime_error("[gctl::loss_func] Invalid array size.");
+
+    for (size_t i = 0; i < tnum_; i++)
+    {
+        diff_[i] = (x[i] - tars_[i])/us_[i];
+    }
+
+    double loss = 0.0;
+    g.resize(tnum_);
+
+    if (ntype_ == L1)
+    {
+        for (size_t i = 0; i < tnum_; i++)
+        {
+            loss += fabs(diff_[i]);
+            if (diff_[i] >= 0.0) g[i] = 1.0/(us_[i]*tnum_);
+            else g[i] = -1.0/(us_[i]*tnum_);
+        }
+    }
+    else if (ntype_ == L2)
+    {
+        for (size_t i = 0; i < tnum_; i++)
+        {
+            loss += diff_[i]*diff_[i];
+            g[i] = 2.0*diff_[i]/(us_[i]*tnum_);
+        }
+    }
+    else throw std::runtime_error("[gctl::loss_func] Invalid measurement type.");
+
+    return loss/tnum_;
 }
-
-double gctl::loss_func::evaluate(double inp, int id)
-{
-    double val = (inp - tars_[id]);
-    if (uncer_type_ == 1) val /= uncer_;
-    else if (uncer_type_ == 2) val /= uncers_[id];
-
-    if (norm_type_ == L1) val = fabs(val);
-    if (norm_type_ == L2) val = val*val;
-    
-    loss_ += val;
-    return val/tar_num_;
-}
-
-double gctl::loss_func::gradient(double inp, int id)
-{
-    double c;
-    if (uncer_type_ == 1) c = uncer_;
-    else if (uncer_type_ == 2) c = uncers_[id];
-
-    double val = (inp - tars_[id]);
-    if (norm_type_ == L1 && val >= 0) val = 1.0;
-    if (norm_type_ == L1 && val < 0)  val = -1.0;
-    if (norm_type_ == L2) val = 2.0*val;
-
-    if (norm_type_ == L1 && uncer_type_ != 0) val /= c;
-    else if (norm_type_ == L2 && uncer_type_ != 0) val /= (c*c);
-
-    return val/tar_num_;
-}
\ No newline at end of file
diff --git a/lib/optimization/loss_func.h b/lib/optimization/loss_func.h
index 2d4be1c..53784a0 100644
--- a/lib/optimization/loss_func.h
+++ b/lib/optimization/loss_func.h
@@ -43,18 +43,14 @@ namespace gctl
         void init(const array<double> &tar, norm_type_e n_type);
         void set_uncertainty(double uncer);
         void set_uncertainty(const array<double> &uncer);
-        double get_loss();
-        double evaluate(double inp, int id);
-        double gradient(double inp, int id);
+        double evaluate(const array<double> &x, array<double> &g);
 
     private:
-        //unsigned int counter_;
-        unsigned int tar_num_;
-        int uncer_type_;
-        double uncer_, loss_;
-        norm_type_e norm_type_;
-        array<double> tars_;
-        array<double> uncers_;
+        bool init_;
+        unsigned int tnum_;
+        norm_type_e ntype_;
+        array<double> tars_, diff_;
+        array<double> us_;
     };
 }