diff --git a/hidimstat/adaptive_permutation_threshold.py b/hidimstat/adaptive_permutation_threshold.py
index 1dc449a..d6dabe5 100644
--- a/hidimstat/adaptive_permutation_threshold.py
+++ b/hidimstat/adaptive_permutation_threshold.py
@@ -50,7 +50,16 @@ def ada_svr(X, y, rcond=1e-3):
 
 
 def _manual_inversion(X, rcond=1e-3):
-    "Inverting taking care of low eigenvalues to increase numerical stability"
+    """
+    Inverting taking care of low eigenvalues to increase numerical stability
+    
+    Parameters
+    -----------
+    X : ndarray, shape (n_features, n_features) 
+        Data.
+        Base on usage of X in the main function, X is squared matrix and not full_ranked (for details see PR#58)
+        
+    """
 
     X = np.asarray(X)
     U, s, V = np.linalg.svd(X, full_matrices=False)