diff --git a/wafo/containers.py b/wafo/containers.py
index 1771053..7e22ca5 100644
--- a/wafo/containers.py
+++ b/wafo/containers.py
@@ -1,7 +1,7 @@
 from __future__ import absolute_import
 import warnings
-from .graphutil import cltext
-from .plotbackend import plotbackend
+from wafo.graphutil import cltext
+from wafo.plotbackend import plotbackend
 from time import gmtime, strftime
 import numpy as np
 from scipy.integrate.quadrature import cumtrapz  # @UnresolvedImport
@@ -166,13 +166,16 @@ class PlotData(object):
         cdf = np.hstack((0, integrate.cumtrapz(self.data, self.args)))
         return PlotData(cdf, np.copy(self.args), xlab='x', ylab='F(x)')
 
-    def integrate(self, a, b, **kwds):
+    def integrate(self, a=None, b=None, **kwds):
         '''
         >>> x = np.linspace(0,5,60)
         >>> d = PlotData(np.sin(x), x)
         >>> d.dataCI = np.vstack((d.data*.9,d.data*1.1)).T
         >>> d.integrate(0,np.pi/2, return_ci=True)
         array([ 0.99940055,  0.85543644,  1.04553343])
+        >>> np.allclose(d.integrate(0, 5, return_ci=True),
+        ...    d.integrate(return_ci=True))
+        True
 
         '''
         method = kwds.pop('method', 'trapz')
@@ -193,6 +196,10 @@ class PlotData(object):
         else:  # One dimensional data
             return_ci = kwds.pop('return_ci', False)
             x = self.args
+            if a is None:
+                a = x[0]
+            if b is None:
+                b = x[-1]
             ix = np.flatnonzero((a < x) & (x < b))
             xi = np.hstack((a, x.take(ix), b))
             fi = np.hstack(
diff --git a/wafo/doc/tutorial_scripts/chapter3.py b/wafo/doc/tutorial_scripts/chapter3.py
index 852d88a..8b159c2 100644
--- a/wafo/doc/tutorial_scripts/chapter3.py
+++ b/wafo/doc/tutorial_scripts/chapter3.py
@@ -47,7 +47,7 @@ plt.show()
 #! Extreme waves - model check: the highest and steepest wave
 #!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 plt.clf()
-S, H = ts.wave_height_steepness(method=0)
+S, H = ts.wave_height_steepness(kind=0)
 indS = S.argmax()
 indH = H.argmax()
 ts.plot_sp_wave([indH, indS],'k.')
@@ -98,7 +98,8 @@ plt.clf()#
 fac = wk.TKDE(Ac,L2=L2)(np.linspace(0.01,3,200), output='plot')
 fac.plot()
 # wafostamp([],'(ER)')
-fac.integrate(a=0.01, b=3)
+print(fac.integrate(a=0.01, b=3))
+print(fac.integrate())
 print('Block = 8'),
 # pause(pstate)
 
@@ -149,7 +150,7 @@ print(mt)
 
 plt.clf()
 S.bandwidth(['alpha'])
-ch, Sa2 = S.characteristic(['Hm0', 'Tm02'])
+ch, Sa2, chtxt = S.characteristic(['Hm0', 'Tm02'])
 
 # disp('Block = 13'), pause(pstate)