update nmae code to allow setting external max and min value

mu_map/eval/measures.py

@@ -7,9 +7,15 @@ def mse(prediction: np.array, target: np.array):
     return mse
 
 
-def nmae(prediction: np.array, target: np.array):
-    mae = np.absolute(prediction - target) / prediction.size
-    nmae = mae.sum() / (target.max() - target.min())
+def nmae(prediction: np.array, target: np.array, vmax:float=None, vmin:float=None):
+    if vmax is None:
+        vmax = target.max()
+    if vmin is None:
+        vmin = target.min()
+
+    ae = np.absolute(prediction - target)
+    mae = ae.sum() / ae.size
+    nmae = mae / (vmax - vmin)
     return nmae