diff --git a/API_reference.md b/API_reference.py
similarity index 95%
rename from API_reference.md
rename to API_reference.py
index c1bb550..798bfd3 100644
--- a/API_reference.md
+++ b/API_reference.py
@@ -65,7 +65,8 @@ eigenvalue_array = guan.calculate_eigenvalue_with_two_parameters(x, y, hamiltoni
 eigenvector = guan.calculate_eigenvector(hamiltonian)
 
 # find vector with the same gauge
-vector_target = find_vector_with_the_same_gauge_with_binary_search(vector_target, vector_ref, show_error=1, show_times=0, show_phase=0, n_test=10001, precision=1e-6)
+vector_target = guan.find_vector_with_the_same_gauge_with_binary_search(vector_target, vector_ref, show_error=1, show_times=0, show_phase=0, n_test=10001, precision=1e-6)
+vector = guan.find_vector_with_fixed_gauge_by_making_one_component_real(vector, precision=0.005)
 
 # calculate Green functions
 green = guan.green_function(fermi_energy, hamiltonian, broadening, self_energy=0)
diff --git a/PyPI/setup.cfg b/PyPI/setup.cfg
index bec272a..b133c04 100644
--- a/PyPI/setup.cfg
+++ b/PyPI/setup.cfg
@@ -1,7 +1,7 @@
 [metadata]
 # replace with your username:
 name = guan
-version = 0.0.7
+version = 0.0.8
 author = guanjihuan
 author_email = guanjihuan@163.com
 description = An open source python package
diff --git a/PyPI/src/guan/find_vector_with_the_same_gauge.py b/PyPI/src/guan/find_vector_with_the_same_gauge.py
index c35af41..13a3e21 100644
--- a/PyPI/src/guan/find_vector_with_the_same_gauge.py
+++ b/PyPI/src/guan/find_vector_with_the_same_gauge.py
@@ -38,4 +38,17 @@ def find_vector_with_the_same_gauge_with_binary_search(vector_target, vector_ref
     vector_target = vector_target*cmath.exp(1j*phase)
     if show_phase==1:
         print('Phase=', phase)   
-    return vector_target
\ No newline at end of file
+    return vector_target
+
+def find_vector_with_fixed_gauge_by_making_one_component_real(vector, precision=0.005):
+    index = np.argmax(np.abs(vector))
+    sign_pre = np.sign(np.imag(vector[index]))
+    for phase in np.arange(0, 2*pi, precision):
+        sign =  np.sign(np.imag(vector[index]*cmath.exp(1j*phase)))
+        if np.abs(np.imag(vector[index]*cmath.exp(1j*phase))) < 1e-9 or sign == -sign_pre:
+            break
+        sign_pre = sign
+    vector = vector*cmath.exp(1j*phase)
+    if np.real(vector[index]) < 0:
+        vector = -vector
+    return vector 
\ No newline at end of file