diff --git a/src/prog/estparam.cpp b/src/prog/estparam.cpp
index 1af717c..e8039e9 100644
--- a/src/prog/estparam.cpp
+++ b/src/prog/estparam.cpp
@@ -76,7 +76,7 @@ void get_jumps(const vector<Path> &paths, vector<Jump> &jumps) {
 }
 
 void get_suff_stat(const vector<Jump> &jumps,
-                   vector<size_t> &tot_freq,
+                   vector<double> &tot_freq,
                    vector<double> &weights) {
   tot_freq.resize(8, 0);
   weights.resize(8, 0);
@@ -91,7 +91,7 @@ void get_suff_stat(const vector<Jump> &jumps,
 
 
 double llk(const vector<Jump> &jumps,
-           const vector<size_t> &tot_freq,
+           const vector<double> &tot_freq,
            const vector<double> &weights,
            const vector<double> &rates) {
   double l = 0;
@@ -103,6 +103,34 @@ double llk(const vector<Jump> &jumps,
 }
 
 
+void grad_llk(const vector<Jump> &jumps,
+              const vector<double> &tot_freq,
+              const vector<double> &weights,
+              const vector<double> &rates,
+              vector<double> &gradient) {
+  gradient.resize(8, 0);
+  
+  gradient[0] = (tot_freq[0] + tot_freq[7])/rates[0] - weights[0] -
+    weights[7]*rates[7]/rates[0];
+
+  gradient[2] = (tot_freq[2] - tot_freq[7])/rates[2] - weights[2] +
+    weights[7]*rates[7]/rates[2];
+
+  gradient[5] = (tot_freq[5] + tot_freq[7])/rates[5] - weights[5] -
+    weights[7]*rates[7]/rates[5];
+
+  gradient[1] = (tot_freq[1] + tot_freq[4] - 2*tot_freq[7])/rates[1] -
+    (weights[1] + weights[4]) + 2*weights[7]*rates[7]/rates[1];
+  
+  gradient[3] = (tot_freq[3] + tot_freq[6] + 2*tot_freq[7])/rates[3] -
+    (weights[3] + weights[6]) - 2*weights[7]*rates[7]/rates[3];
+
+  gradient[4] = gradient[1];
+  gradient[6] = gradient[3];
+  // gradient[7] remains 0, and rates[7] is determined by other rates.
+}
+
+
 void est_trans_prob(const vector<bool> &seq,
                     vector<vector<double> > & trans_prob) {
   double c00(0), c01(0), c10(0), c11(0), c0(0), c1(1);
@@ -203,7 +231,7 @@ int main(int argc, const char **argv) {
     if (!param_file.empty()) {
       model_param p;
       read_param(param_file, p);
-      vector<size_t> tot_freq;
+      vector<double> tot_freq;
       vector<double> weights;
       get_suff_stat(jumps, tot_freq, weights);
 
@@ -230,6 +258,20 @@ int main(int argc, const char **argv) {
         for (size_t i = 0; i < rates.size(); ++i) cerr << rates[i] << "\t";        
         cerr << endl;
         cerr << "log-likelihood= " << llk(jumps, tot_freq, weights, rates) << endl;
+
+        cerr << "tot_freq:" << endl;
+        for (size_t i =0; i < 8; ++i)
+          cerr << "[" << i << "]\t" << tot_freq[i] << endl;
+        
+        cerr << "weights:" << endl;
+        for (size_t i =0; i < 8; ++i)
+          cerr << "[" << i << "]\t" << weights[i] << endl;
+        
+        vector<double> gradient;
+        grad_llk(jumps, tot_freq, weights, rates, gradient);
+        cerr << "gradient :" << endl;
+        for (size_t i =0; i < gradient.size(); ++i)
+          cerr << "[" << i << "]\t" << gradient[i] << endl;
       }
       
     }