diff --git a/src/histogram_transfer/pdf_transfer_1d.py b/src/histogram_transfer/pdf_transfer_1d.py
index 71e0925..e551c37 100644
--- a/src/histogram_transfer/pdf_transfer_1d.py
+++ b/src/histogram_transfer/pdf_transfer_1d.py
@@ -1,13 +1,24 @@
 import numpy as np
 
 
-def pdf_transfer_1d(pX: np.ndarray, pY: np.ndarray) -> np.ndarray:
-    PX = np.cumsum(pX + np.finfo(float).eps)
-    PX /= PX[-1]
+EPSILON = np.finfo(float).eps
 
-    PY = np.cumsum(pY + np.finfo(float).eps)
-    PY /= PY[-1]
 
-    f = np.interp(PX, PY, np.arange(len(pX)))
+def pdf_transfer_1d(
+    source_y: np.ndarray, target_y: np.ndarray, target_x: np.ndarray = None
+) -> np.ndarray:
+    """
+    return the best source_x-es
+    """
+    cumulative_source = np.cumsum(source_y).astype(np.float64)
+    cumulative_source /= cumulative_source[-1]
 
-    return f
+    cumulative_target = np.cumsum(target_y).astype(np.float64)
+    cumulative_target /= cumulative_target[-1]
+
+    cumulative_transfered = np.interp(
+        cumulative_source,
+        cumulative_target,
+        np.arange(len(cumulative_source)) if target_x is None else target_x,
+    )
+    return cumulative_transfered