diff --git a/wafo/containers.py b/wafo/containers.py
index 661b165..34986a3 100644
--- a/wafo/containers.py
+++ b/wafo/containers.py
@@ -168,7 +168,7 @@ class PlotData(object):
         >>> ci = PlotData(np.vstack((y*.9, y*1.1)).T, x)
         >>> d = PlotData(y, x, children=[ci])
         >>> d.integrate(0, np.pi/2, return_ci=True)
-        array([ 0.99940055,  0.85543644,  1.04553343])
+        array([ 0.99940055,  0.89946049,  1.0993406 ])
         >>> np.allclose(d.integrate(0, 5, return_ci=True),
         ...    d.integrate(return_ci=True))
         True
diff --git a/wafo/interpolate.py b/wafo/interpolate.py
index b3526e0..105ddd3 100644
--- a/wafo/interpolate.py
+++ b/wafo/interpolate.py
@@ -618,7 +618,8 @@ class SmoothSpline(PPform):
 
         return coefs, x
 
-    def _compute_u(self, p, D, dydx, dx, dx1, n):
+    @staticmethod
+    def _compute_u(p, D, dydx, dx, dx1, n):
         if p is None or p != 0:
             data = [dx[1:n - 1], 2 * (dx[:n - 2] + dx[1:n - 1]), dx[:n - 2]]
             R = sparse.spdiags(data, [-1, 0, 1], n - 2, n - 2)
@@ -1345,7 +1346,7 @@ def test_pp():
 
 def test_docstrings():
     import doctest
-    print('Testing docstrings in %s' % __file__)
+    print('Testing docstrings in {}'.formate(__file__))
     doctest.testmod(optionflags=doctest.NORMALIZE_WHITESPACE)