diff --git a/src/lib/lbfgs.c b/src/lib/lbfgs.c
index e037e8b..93cc64e 100644
--- a/src/lib/lbfgs.c
+++ b/src/lib/lbfgs.c
@@ -268,9 +268,11 @@ int lbfgs(
     lbfgsfloatval_t *xp = NULL;
     lbfgsfloatval_t *g = NULL, *gp = NULL, *pg = NULL; // gp (p for previous) pg (p for pesudo)
     lbfgsfloatval_t *d = NULL, *w = NULL, *pf = NULL;
-    lbfgsfloatval_t *dp = NULL; // p for preconditioned
+    lbfgsfloatval_t *dp = NULL; // p for preconditioned (Add by Yi Zhang on 02-16-2022)
+    lbfgsfloatval_t *y2 = NULL; // Add by Yi Zhang on 02-16-2022
     iteration_data_t *lm = NULL, *it = NULL;
     lbfgsfloatval_t ys, yy;
+    lbfgsfloatval_t Yk; // Add by Yi Zhang on 02-16-2022
     lbfgsfloatval_t xnorm, gnorm, beta;
     lbfgsfloatval_t fx = 0.;
     lbfgsfloatval_t rate = 0.;
@@ -384,6 +386,13 @@ int lbfgs(
         goto lbfgs_exit;
     }
 
+    // Add by Yi Zhang on 02-16-2022
+    y2 = (lbfgsfloatval_t*)vecalloc(n * sizeof(lbfgsfloatval_t));
+    if (y2 == NULL) {
+        ret = LBFGSERR_OUTOFMEMORY;
+        goto lbfgs_exit;
+    }
+
     if (cd.proc_precondition) {
         dp = (lbfgsfloatval_t*)vecalloc(n * sizeof(lbfgsfloatval_t));
         if (dp == NULL) {
@@ -391,6 +400,7 @@ int lbfgs(
             goto lbfgs_exit;
         }
     }
+    // End
 
     // 初始化计算L1模的数组
     if (param.orthantwise_c != 0.) {
@@ -625,9 +635,13 @@ int lbfgs(
             vecadd(d, it->y, -it->alpha, n);
         }
 
-        vecscale(d, ys / yy, n); // 适当缩放d的大小
+        // Annotated by Yi Zhang on 02-16-2022
+        //vecscale(d, ys / yy, n); // 适当缩放d的大小
 
-        // 我们在这里提供一个预优函数的接口 返回 d = H0^-1 * d
+        // Add by Yi Zhang on 02-16-2022
+        // Wah June Leong & Chuei Yee Chen (2013) A class of diagonal preconditioners for limited memory BFGS method, 
+        // Optimization Methods and Software, 28:2, 379-392, DOI: 10.1080/10556788.2011.653356
+        // 我们在这里提供一个预优函数的接口 需还原则删除下面的代码段 同时取消上面一行注释
         if (cd.proc_precondition) {
             if (param.orthantwise_c == 0.) {
                 cd.proc_precondition(cd.instance, x, g, d, dp, n);
@@ -636,7 +650,15 @@ int lbfgs(
             }
             
             veccpy(d, dp, n);
+        } else if (ys < yy) {
+            vecscale(d, ys / yy, n); // 适当缩放d的大小
+        } else {
+            veccpy(y2, lm[end].y, n);
+            vecmul(y2, lm[end].y, n);
+            vecdot(&Yk, y2, y2, n);
+            vecadd(d, y2, (ys-yy)/Yk, n);
         }
+        // End
 
         for (i = 0;i < bound;++i) {
             it = &lm[j];
@@ -688,6 +710,14 @@ lbfgs_exit:
     vecfree(g);
     vecfree(xp);
 
+    // Add by Yi Zhang on 02-16-2022
+    vecfree(y2);
+
+    if (cd.proc_precondition) {
+        vecfree(dp);
+    }
+    // End
+
     return ret;
 }
 
diff --git a/src/sample/sample4.cpp b/src/sample/sample4.cpp
index 32dcb6b..ad31406 100644
--- a/src/sample/sample4.cpp
+++ b/src/sample/sample4.cpp
@@ -8,6 +8,7 @@
 using std::clog;
 using std::endl;
 
+#define M 120
 #define N 100
 
 inline lbfgsfloatval_t scalernd(lbfgsfloatval_t l, lbfgsfloatval_t h)
@@ -79,32 +80,29 @@ private:
 
 TEST_FUNC::TEST_FUNC()
 {
-	kernel = new lbfgsfloatval_t* [N];
-    for (size_t i = 0; i < N; i++)
+	kernel = new lbfgsfloatval_t* [M];
+    for (size_t i = 0; i < M; i++)
     {
         kernel[i] =  new lbfgsfloatval_t [N];
     }
     
     x = new lbfgsfloatval_t [N];
     m = new lbfgsfloatval_t [N];
-    mid = new lbfgsfloatval_t [N];
-    d = new lbfgsfloatval_t [N];
+    mid = new lbfgsfloatval_t [M];
+    d = new lbfgsfloatval_t [M];
 
     srand(time(nullptr));
-    for (size_t i = 0; i < N-1; i++)
+    for (size_t i = 0; i < M; i++)
     {
-        for (size_t j = i+1; j < N; j++)
+        for (size_t j = 0; j < N; j++)
         {
-            kernel[i][j] = scalernd(0.0, 2.0);
-            kernel[j][i] = kernel[i][j];
+            kernel[i][j] = scalernd(-2.0, 2.0);
         }
-
-        kernel[i][i] = scalernd(10.0, 20.0);
     }
 
     vecrnd(m, 1.0, 2.0, N);
 
-    for (size_t i = 0; i < N; i++)
+    for (size_t i = 0; i < M; i++)
     {
         d[i] = 0.0;
         for (size_t j = 0; j < N; j++)
@@ -131,7 +129,7 @@ TEST_FUNC::~TEST_FUNC()
 lbfgsfloatval_t TEST_FUNC::Func(const lbfgsfloatval_t *x, lbfgsfloatval_t *g,
 		const int n, const lbfgsfloatval_t step)
 {
-    for (size_t i = 0; i < N; i++)
+    for (size_t i = 0; i < M; i++)
     {
         mid[i] = 0.0;
         for (size_t j = 0; j < N; j++)
@@ -150,7 +148,7 @@ lbfgsfloatval_t TEST_FUNC::Func(const lbfgsfloatval_t *x, lbfgsfloatval_t *g,
     for (size_t j = 0; j < N; j++)
     {
         g[j] = 0.0;
-        for (size_t i = 0; i < N; i++)
+        for (size_t i = 0; i < M; i++)
         {
             g[j] += kernel[i][j]*mid[i];
         }
@@ -171,7 +169,12 @@ void TEST_FUNC::Precondition(const lbfgsfloatval_t *x, const lbfgsfloatval_t *g,
 {
     for (size_t j = 0; j < N; j++)
     {
-        d_pre[j] = d[j]/kernel[j][j];
+        d_pre[j] = 0.0;
+        for (size_t i = 0; i < M; i++)
+        {
+            d_pre[j] += kernel[i][j]*kernel[i][j];
+        }
+        d_pre[j] = d[j]/d_pre[j];
     }
     return;
 }
@@ -183,9 +186,8 @@ int TEST_FUNC::Routine()
 	lbfgs_parameter_t self_para;
 	lbfgs_parameter_init(&self_para);
 	self_para.epsilon = 1e-7;
-    self_para.max_linesearch = 1000;
 
-	int ret = lbfgs(N, x, &fx, _Func, _Progress, this, &self_para, _Precondition);
+	int ret = lbfgs(N, x, &fx, _Func, _Progress, this, &self_para, NULL);
 
 	clog << endl << "L-BFGS optimization terminated with status: " << lbfgs_strerror(ret) << endl;
     clog << "Maximal difference = " << max_diff(x, m, N) << endl;